Claim and Claim Adjustment Expense Reserves (Net Prior Year Development) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Segment Reporting [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	$ 91	$ 108	$ 191	$ 191
Specialty | Property and Casualty Segments
Segment Reporting [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	(1)	0	44	10
Commercial | Property and Casualty Segments
Segment Reporting [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	(5)	(4)	50	47
International | Property and Casualty Segments
Segment Reporting [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	0	0	0	0
Corporate & Other
Segment Reporting [Line Items]
Pretax (favorable) unfavorable premium development, excluding Life & Group	$ 97	$ 112	$ 97	$ 134