Capital Stock and Earnings Per Share (OMH Only) - Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator (basic and diluted):
Net income	$ 194	$ 185	$ 476	$ 696
Denominator:
Weighted average number of shares outstanding (basic) (in shares)	120,407,889	123,352,522	120,571,103	124,989,263
Effect of dilutive securities (in shares)	346,805	216,098	219,382	253,943
Weighted average number of shares outstanding (diluted) (in shares)	120,754,694	123,568,620	120,790,485	125,243,206
Earnings per share:
Basic (in dollars per share)	$ 1.61	$ 1.50	$ 3.95	$ 5.56
Diluted (in dollars per share)	$ 1.61	$ 1.49	$ 3.94	$ 5.55
Restricted stock units
Earnings per share:
Shares excluded in the diluted earnings per share calculation (in shares)	886,333	1,278,052	933,663	1,230,739