Capital Stock and Earnings Per Share (OMH Only) - Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator (basic and diluted):
Net income	$ 641	$ 872	$ 1,314
Denominator:
Weighted average number of shares outstanding (basic) (in shares)	120,382,227	124,178,643	132,653,889
Effect of dilutive securities (in shares)	247,363	238,631	400,605
Weighted average number of shares outstanding (diluted) (in shares)	120,629,590	124,417,274	133,054,494
Earnings per share:
Basic (in dollars per share)	$ 5.33	$ 7.02	$ 9.91
Diluted (in dollars per share)	$ 5.32	$ 7.01	$ 9.88
Restricted stock units
Earnings per share:
Shares excluded in the diluted earnings per share calculation (in shares)	1,048,970	1,335,442	421,511