Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) (Details) - Reclassifications - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss)
Reclassification adjustment impacting net realized investment gains (losses) on the income statement	$ 204	$ (171)	$ (2)
Reclassification adjustment impacting claims and claim adjustment expenses on the income statement	22,854	20,298	19,123
Reclassification adjustment impacting general and administrative expense on the income statement	4,810	4,677	4,509
Total reclassifications	(3,354)	(4,458)	(3,237)
Income tax (expense) benefit	(512)	(796)	(540)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	(2,842)	(3,662)	(2,697)
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	139	35	32
Income tax (expense) benefit	29	7	7
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	110	28	25
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 income statement	98	(67)	(52)
Income tax (expense) benefit	21	(14)	(11)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	77	(53)	(41)
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 income statement	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 on the income statement	17	41	35
Reclassification adjustment impacting general and administrative expense on the income statement	24	61	50
Total reclassifications	41	102	85
Income tax (expense) benefit	8	21	18
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	33	81	67
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 income statement	0	0	(1)
Income tax (expense) benefit	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	$ 0	$ 0	$ (1)