Earnings Per Share - Computation of Basic and Diluted Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income from continuing operations	$ 310	$ 187	$ 1,296	$ 105
Less: Net income attributable to non-controlling interests	0	5	0	2
Less: Undistributed earnings from continuing operations attributable to participating stockholders	1	2	9	1
Less: Premium on retirement of preferred stock	28	0	28	0
Net income from continuing operations attributable to Mr. Cooper common stockholders	281	180	1,259	102
Net (loss) income from discontinued operations	(11)	27	3	11
Less: Undistributed earnings from discontinued operations attributable to participating stockholders	0	0	0	0
Net (loss) income from discontinued operations attributable to Mr. Cooper common stockholders	(11)	27	3	11
Net income	299	214	1,299	116
Less: Net earnings attributable to non-controlling interests	0	5	0	2
Net income attributable to Mr. Cooper	299	209	1,299	114
Less: Undistributed earnings attributable to participating stockholders	1	2	9	1
Net income attributable to common stockholders	$ 270	$ 207	$ 1,262	$ 113
Earnings Per Share, Basic [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 3.56	$ 1.98	$ 14.85	$ 1.12
Income (Loss) from Continuing Operations, Per Diluted Share	3.42	1.91	14.20	1.09
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	(0.14)	0.28	0.04	0.11
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	(0.13)	0.27	0.03	0.11
Basic (in dollars per share)	3.42	2.26	14.89	1.23
Diluted (in dollars per share)	$ 3.29	$ 2.18	$ 14.23	$ 1.20
Weighted average shares of common stock outstanding (in thousands):
Basic (in shares)	78,944	91,682	84,809	91,688
Dilutive effect of stock awards (in shares)	2,826	2,563	3,176	1,529
Dilutive effect of participating securities (in shares)	301	839	658	839
Diluted (in shares)	82,071	95,084	88,643	94,056