Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) (Details) - Reclassifications - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment gains (losses) on the income statement	$ 95	$ (61)	$ 118	$ (105)
Reclassification adjustment impacting claims and claim adjustment expenses on the income statement	5,803	5,045	10,842	10,015
Reclassification adjustment impacting general and administrative expense on the income statement	1,223	1,174	2,414	2,337
Total reclassifications	(657)	(1,131)	(1,839)	(2,022)
Income tax (expense) benefit	(106)	(197)	(270)	(355)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	(551)	(934)	(1,569)	(1,667)
Accumulated Other Comprehensive Income (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Total reclassifications	32	2	40	13
Income tax (expense) benefit	8	1	9	3
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	24	1	31	10
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 (losses) on the income statement	21	(24)	19	(38)
Income tax (expense) benefit	5	(5)	4	(8)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	16	(19)	15	(30)
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 (losses) on the income statement	0	0	0	0
Income tax (expense) benefit	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	0	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	4	11	8	21
Reclassification adjustment impacting general and administrative expense on the income statement	7	15	13	30
Total reclassifications	11	26	21	51
Income tax (expense) benefit	3	6	5	11
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	8	20	16	40
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 (losses) on the income statement	0	0	0	0
Income tax (expense) benefit	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	$ 0	$ 0	$ 0	$ 0