Other Comprehensive Income - Tax effects on components of other comprehensive income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Before tax amount:
Unrealized holding gains (losses) arising during period, before tax	$ 617	$ (2,009)	$ (408)
Less reclassification of net realized gains (losses) included in net income, before tax	(428)	(279)	155
Foreign currency translation adjustments, before tax	23	(56)	(65)
Other comprehensive income (loss), before tax	1,068	(1,786)	(628)
Tax expense (benefit):
Unrealized holding gains (losses) arising during period, tax	70	(237)	(22)
Less reclassification of net realized gains (losses) included in net income, tax	(28)	(32)	38
Foreign currency translation adjustments, tax	0	0	0
Other comprehensive income (loss), tax	98	(205)	(60)
Net of tax amount:
Unrealized holding gains (losses) arising during period, net of tax	547	(1,772)	(386)
Less reclassification of net realized gains (losses) included in net income, net of tax	(400)	(247)	117
Foreign currency translation adjustments, net of tax	23	(56)	(65)
Net current period other comprehensive income (loss)	$ 970	$ (1,581)	$ (568)