The 58-year-old Oscar-winning actor petitioned on Tuesday to end her marriage to the 57-year-old Grammy-winning country singer in a Nashville court. The documents state the couple has undergone "marital difficulties and irreconcilable differences".
Kidman and Urban, two of the biggest stars to come out of Australia in recent decades, have been red carpet fixtures throughout their two-decade relationship, with Urban joining his wife at the Oscars and Kidman attending music events like the Academy of Country Music Awards.
The filings include a marriage dissolution and childcare plan agreed on by the couple and submitted for a judge's approval.
"The mother and father will behave with each other and each child so as to provide a loving, stable, consistent and nurturing relationship with the child even though they are divorced," says the permanent parenting plan, using language common in the state's divorces.
"They will not speak badly of each other or the members of the family of the other parent. They will encourage each child to continue to love the other parent and be comfortable in both families."
The plan asks that Kidman be the primary residential parent to the couple's two daughters, ages 17 and 14, having them for 306 days per year with Urban taking them for the other 59.
The girls have lived in Nashville, Tennessee all their lives, and the documents give no indication that will change.
The filing states that each parent earns more than $US100,000 per month and neither will need childcare or spousal support.
The marriage dissolution plan lays out a roughly equal division of joint assets, with each keeping all the assets that are in their own name, including the copyrights and royalties for their artistic work.
The detailed agreements suggests that the divorce had been in the works for well over a month at the least. Urban signed the parenting plan on August 29, Kidman on September 6.
It will take at least 90 days for the divorce to become final under Tennessee law.
Representatives for Kidman and Urban did not respond to emailed requests for comment on Tuesday.
Both raised in Australia, Kidman and Urban met in 2005 at a Los Angeles event honouring Australians and were married in Sydney the following year.
The marriage was the first for Urban and the second for Kidman, who was married to Tom Cruise from 1990 to 2001. Kidman also has two older children with Cruise.
The couple had publicly but lovingly described some marital difficulties, but there were still few if any signs they were headed for divorce. Media reports of their separation came just a day before the divorce filing.
Last year at the premiere of the Netflix series The Perfect Couple, Kidman told The Associated Press the term didn't apply to her and Urban.
"You're heading for trouble if you consider yourselves the perfect couple," she said. "I'm not a believer in perfect."
A few months earlier, Urban paid tribute to Kidman, and brought her to tears, when she received the AFI Life Achievement Award.
Urban said she showed him "what love in action really looks like" when his substance abuse problems emerged almost immediately after they wed in 2006.
"Four months into our marriage, I'm in rehab for three months," Urban said. "Nic pushed through every negative voice, I'm sure even some of her own, and she chose love. And here we are 18 years later."
Kidman's film roles have included Days of Thunder, Eyes Wide Shut, Moulin Rouge and The Hours, for which she won an Academy Award for playing author Virginia Woolf. She has more recently worked in television, including the series Nine Perfect Strangers and Big Little Lies, for which she won Emmys as both actor and producer.
Urban has been a major country star since the 1990s, with hits including Somebody Like You and Blue Ain't Your Color. He has won four Grammy Awards and more than a dozen Academy of Country Music Awards.
Their split was first reported by TMZ.
