Other Comprehensive Income and Accumulated Other Comprehensive Income (Details) - Reclassifications - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment gains on the income statement	$ (171)	$ (2)	$ (113)
Reclassification adjustment impacting claims and claim adjustment expenses on the income statement	20,298	19,123	19,133
Reclassification adjustment impacting general and administrative expense on the income statement	4,677	4,509	4,365
Total reclassifications	(4,458)	(3,237)	(3,138)
Income tax (expense) benefit	(796)	(540)	(516)
Amounts reclassified from accumulated other comprehensive income, net of taxes	(3,662)	(2,697)	(2,622)
Accumulated Other Comprehensive Income (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Total reclassifications	35	32	4
Income tax (expense) benefit	7	7	(1)
Amounts reclassified from accumulated other comprehensive income, net of taxes	28	25	5
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 [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment gains on the income statement	(67)	(52)	(55)
Income tax (expense) benefit	(14)	(11)	(12)
Amounts reclassified from accumulated other comprehensive income, net of taxes	(53)	(41)	(43)
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 [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment gains on the income statement	0	0	0
Income tax (expense) benefit	0	0	0
Amounts reclassified from accumulated other comprehensive income, net of taxes	0	0	0
Net Benefit Plan Assets and Obligations Recognized in Shareholders’ Equity [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting claims and claim adjustment expenses on the income statement	41	35	21
Reclassification adjustment impacting general and administrative expense on the income statement	61	50	31
Total reclassifications	102	85	52
Income tax (expense) benefit	21	18	11
Amounts reclassified from accumulated other comprehensive income, net of taxes	81	67	41
Net Unrealized Foreign Currency Translation [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment gains on the income statement	0	(1)	7
Income tax (expense) benefit	0	0	0
Amounts reclassified from accumulated other comprehensive income, net of taxes	$ 0	$ (1)	$ 7