Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Current
Federal					$ 769	$ (1,859)	$ 1,774
State					114	(1)	281
Foreign					12	16	22
Total					895	(1,844)	2,077
Deferred
Federal					(376)	2,100	(1,166)
State					(72)	78	(123)
Foreign					(5)	(5)	1
Total					(453)	2,173	(1,288)
Provision for income taxes	$ 73	$ 174	$ 63	$ 132	$ 442	$ 329	$ 789