Segment Information - Reconciliation of Revenue from Segments to Consolidated (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]
Earned premiums and fee income	$ 6,365	$ 6,047	$ 12,597	$ 11,968
Net investment income	800	658	1,534	1,310
Realized Investment Gains (Losses)	64	(19)	12	(68)
Other Income	34	30	61	52
Total revenues	7,263	6,716	14,204	13,262
P&C Personal Insurance \| AARP Members [Member]
Segment Reporting [Line Items]
Earned premiums and fee income	798	841	1,600	1,660
Operating Segments [Member]
Segment Reporting [Line Items]
Earned premiums and fee income	6,354	6,037	12,576	11,947
Net investment income	782	644	1,500	1,282
Realized Investment Gains (Losses)	26	(42)	(9)	(72)
Other Income	26	25	48	46
Total revenues	7,188	6,664	14,115	13,203
Operating Segments [Member] \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	3,675	3,435	7,259	6,770
Net investment income	556	449	1,061	886
Realized Investment Gains (Losses)	12	(20)	(7)	(44)
Other Income	1	1	1	2
Total revenues	4,244	3,865	8,314	7,614
Operating Segments [Member] \| P&C Personal Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	912	939	1,827	1,846
Net investment income	67	58	129	115
Realized Investment Gains (Losses)	4	(4)	0	(6)
Other Income	25	24	47	44
Total revenues	1,008	1,017	2,003	1,999
Operating Segments [Member] \| Property & Casualty Other Operations [Member]
Segment Reporting [Line Items]
Earned premiums and fee income	0	0	0	0
Net investment income	22	19	42	37
Realized Investment Gains (Losses)	1	(2)	0	(2)
Other Income	0	0	0	0
Total revenues	23	17	42	35
Operating Segments [Member] \| Employee Benefits [Member]
Segment Reporting [Line Items]
Earned premiums and fee income	1,767	1,663	3,490	3,331
Net investment income	137	118	268	244
Realized Investment Gains (Losses)	9	(16)	(2)	(20)
Other Income	0	0	0	0
Total revenues	1,913	1,765	3,756	3,555
Operating Segments [Member] \| Workers' Compensation \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	933	917	1,854	1,835
Operating Segments [Member] \| General liability \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	669	609	1,310	1,193
Operating Segments [Member] \| Marine \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	73	68	145	137
Operating Segments [Member] \| Package business \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	718	659	1,424	1,278
Operating Segments [Member] \| Property \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	383	355	755	694
Operating Segments [Member] \| Property \| P&C Personal Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	320	305	637	588
Operating Segments [Member] \| Professional liability \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	210	208	425	414
Operating Segments [Member] \| Bond \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	90	83	173	168
Operating Segments [Member] \| Assumed reinsurance \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	236	222	466	442
Operating Segments [Member] \| Automobile \| P&C Business Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	363	314	707	609
Operating Segments [Member] \| Automobile \| P&C Personal Insurance
Segment Reporting [Line Items]
Earned premiums and fee income	592	634	1,190	1,258
Operating Segments [Member] \| Group disability \| Employee Benefits [Member]
Segment Reporting [Line Items]
Earned premiums and fee income	980	899	1,907	1,799
Operating Segments [Member] \| Group life \| Employee Benefits [Member]
Segment Reporting [Line Items]
Earned premiums and fee income	652	644	1,313	1,294
Operating Segments [Member] \| Other \| Employee Benefits [Member]
Segment Reporting [Line Items]
Earned premiums and fee income	$ 135	$ 120	$ 270	$ 238