Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) (Details) - Reclassifications - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Reclassification adjustment impacting net realized investment gains (losses) on the income statement	$ (6)	$ 23
Reclassification adjustment impacting claims and claim adjustment expenses (benefit) on the income statement	5,959	5,039
Reclassification adjustment impacting general and administrative expenses (benefit) on the income statement	1,267	1,191
Total reclassifications	(928)	(1,182)
Income tax (expense) benefit	47	(164)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	(975)	(1,018)
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	8	8
Income tax (expense) benefit	2	1
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	6	7
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
Reclassification adjustment impacting net realized investment gains (losses) on the income statement	11	(2)
Income tax (expense) benefit	2	(1)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	9	(1)
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
Reclassification adjustment impacting net realized investment gains (losses) on the income statement	0	0
Income tax (expense) benefit	0	0
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	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 income statement	(1)	4
Reclassification adjustment impacting general and administrative expenses (benefit) on the income statement	(2)	6
Total reclassifications	(3)	10
Income tax (expense) benefit	0	2
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	(3)	8
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 gains (losses) on the income statement	0	0
Income tax (expense) benefit	0	0
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes	$ 0	$ 0