Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) (Details) - Reclassifications - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss)
Reclassification adjustment impacting net realized investment losses on the consolidated statement of income	$ 30	$ 105	$ 204
Reclassification adjustment impacting claims and claim adjustment expenses (benefit) on the consolidated statement of income	27,059	26,215	22,854
Reclassification adjustment impacting general and administrative expenses (benefit) on the consolidated statement of income	5,819	5,176	4,810
Total reclassifications	(6,180)	(3,371)	(3,354)
Income tax (expense) benefit	(1,181)	(380)	(512)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	(4,999)	(2,991)	(2,842)
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	126	83	139
Income tax (expense) benefit	26	17	29
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	100	66	110
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 losses on the consolidated statement of income	131	96	98
Income tax (expense) benefit	27	20	21
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	104	76	77
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 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	(2)	(5)	17
Reclassification adjustment impacting general and administrative expenses (benefit) on the consolidated statement of income	(3)	(8)	24
Total reclassifications	(5)	(13)	41
Income tax (expense) benefit	(1)	(3)	8
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	(4)	(10)	33
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 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