Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) (Details) - Reclassifications - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss)
Reclassification adjustment impacting net realized investment gains (losses) on the consolidated statement of income	$ 105	$ 204	$ (171)
Reclassification adjustment impacting claims and claim adjustment expenses (benefit) on the consolidated statement of income	26,215	22,854	20,298
Reclassification adjustment impacting general and administrative expenses (benefit) on the consolidated statement of income	5,176	4,810	4,677
Total reclassifications	(3,371)	(3,354)	(4,458)
Income tax (expense) benefit	(380)	(512)	(796)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	(2,991)	(2,842)	(3,662)
Accumulated Other Comprehensive Income (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss)
Total reclassifications	83	139	35
Income tax (expense) benefit	17	29	7
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	66	110	28
Changes in Net Unrealized Gains (Losses) on Investment Securities Having No Credit Losses Recognized in the Consolidated Statement of Income [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss)
Reclassification adjustment impacting net realized investment gains (losses) on the consolidated statement of income	96	98	(67)
Income tax (expense) benefit	20	21	(14)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	76	77	(53)
Changes in Net Unrealized Gains (Losses) on Investment Securities Having Credit Losses Recognized in the Consolidated Statement of Income [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss)
Reclassification adjustment impacting net realized investment gains (losses) on the consolidated statement of income	0	0	0
Income tax (expense) benefit	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	0	0	0
Net Benefit Plan Assets and Obligations Recognized in Shareholders’ Equity [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss)
Reclassification adjustment impacting claims and claim adjustment expenses (benefit) on the consolidated statement of income	(5)	17	41
Reclassification adjustment impacting general and administrative expenses (benefit) on the consolidated statement of income	(8)	24	61
Total reclassifications	(13)	41	102
Income tax (expense) benefit	(3)	8	21
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	(10)	33	81
Net Unrealized Foreign Currency Translation [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss)
Reclassification adjustment impacting net realized investment gains (losses) on the consolidated statement of income	0	0	0
Income tax (expense) benefit	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	$ 0	$ 0	$ 0