Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Treasury Shares Amount	Total Nationstar Stockholders’ Equity and Mr. Cooper Stockholders’ Equity, respectively	Total Nationstar Stockholders’ Equity and Mr. Cooper Stockholders’ Equity, respectively Cumulative Effect, Period of Adoption, Adjustment	Non-controlling Interests
Beginning balance (in shares) at Dec. 31, 2017			0	97,728
Beginning balance at Dec. 31, 2017	$ 1,722		$ 0	$ 1	$ 1,131	$ 731		$ (148)	$ 1,715		$ 7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued / (surrendered) under incentive compensation plan (in shares)				450
Shares issued / (surrendered) under incentive compensation plan	(9)				(6)			(3)	(9)
Share-based compensation	17				17				17
Dividends to non-controlling interests	(1)				5				5		(6)
Net income	154					154			154
Ending balance (in shares) at Jul. 31, 2018			0	98,178
Ending balance at Jul. 31, 2018	1,883		$ 0	$ 1	1,147	885		(151)	1,882		1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	884
Ending balance (in shares) at Dec. 31, 2018			1,000	90,821
Ending balance at Dec. 31, 2018	1,945		$ 0	$ 1	1,093	848		0	1,942		3
Beginning balance (in shares) at Aug. 01, 2018			1,000	90,806
Beginning balance at Aug. 01, 2018	1,056		$ 0	$ 1	1,091	(36)		0	1,056		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Non-controlling interests acquired	3										3
Shares issued / (surrendered) under incentive compensation plan (in shares)				15
Share-based compensation	2				2				2
Net income	884					884			884
Ending balance (in shares) at Dec. 31, 2018			1,000	90,821
Ending balance at Dec. 31, 2018	1,945		$ 0	$ 1	1,093	848		0	1,942		3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued / (surrendered) under incentive compensation plan (in shares)				297
Shares issued / (surrendered) under incentive compensation plan	(2)				(2)				(2)
Share-based compensation	$ 18				18				18
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Net income	$ 270					274			274		(4)
Ending balance (in shares) at Dec. 31, 2019			1,000	91,118
Ending balance at Dec. 31, 2019	2,231	$ 7	$ 0	$ 1	1,109	1,122	$ 7	0	2,232	$ 7	(1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued / (surrendered) under incentive compensation plan (in shares)				923
Shares issued / (surrendered) under incentive compensation plan	(5)				(5)				(5)
Share-based compensation	22				22				22
Repurchase of common stock (in shares)				(2,584)
Repurchase of common stock	(58)							(58)	(58)
Net income	307					305			305		2
Ending balance (in shares) at Dec. 31, 2020			1,000	89,457
Ending balance at Dec. 31, 2020	$ 2,504		$ 0	$ 1	$ 1,126	$ 1,434		$ (58)	$ 2,503		$ 1