Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) (Details) - Reclassifications - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment losses on the consolidated statement of income (loss)	$ 35	$ 95	$ 29	$ 118
Reclassification adjustment impacting claims and claim adjustment expenses (benefit) on the consolidated statement of income (loss)	7,227	5,803	13,186	10,842
Reclassification adjustment impacting general and administrative expenses (benefit) on the consolidated statement of income (loss)	1,308	1,223	2,575	2,414
Total reclassifications	48	(657)	(880)	(1,839)
Income tax (expense) benefit	34	(106)	81	(270)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	14	(551)	(961)	(1,569)
Accumulated Other Comprehensive Income (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Total reclassifications	19	32	27	40
Income tax (expense) benefit	4	8	6	9
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	15	24	21	31
Changes in Net Unrealized Gains (Losses) on Investment Securities Having No Credit Losses Recognized in the Consolidated Statement of Income (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment losses on the consolidated statement of income (loss)	22	21	33	19
Income tax (expense) benefit	5	5	7	4
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	17	16	26	15
Changes in Net Unrealized Gains (Losses) on Investment Securities Having Credit Losses Recognized in the Consolidated Statement of Income (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment losses on the consolidated statement of income (loss)	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 (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting claims and claim adjustment expenses (benefit) on the consolidated statement of income (loss)	(1)	4	(2)	8
Reclassification adjustment impacting general and administrative expenses (benefit) on the consolidated statement of income (loss)	(2)	7	(4)	13
Total reclassifications	(3)	11	(6)	21
Income tax (expense) benefit	(1)	3	(1)	5
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	(2)	8	(5)	16
Net Unrealized Foreign Currency Translation [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment losses on the consolidated statement of income (loss)	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