Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net earned premiums	$ 1,381	$ 1,442	$ 3,774	$ 3,815
Net investment income	572	588	1,584	1,710
Other income	45	58	153	170
Revenues before realized gains (losses)	2,045	2,141	5,618	5,885
Realized gains (losses) on securities	45	(18)	(302)	222
Realized losses on subsidiaries	(30)	0	(30)	0
Total revenues	2,060	2,123	5,286	6,107
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net earned premiums	1,381	1,442	3,774	3,815
Net investment income	112	124	277	352
Other income	0	5	8	10
Revenues before realized gains (losses)	1,493	1,571	4,059	4,177
Annuity
Segment Reporting Information [Line Items]
Net investment income	464	448	1,270	1,334
Other income	30	32	95	90
Revenues before realized gains (losses)	494	480	1,365	1,424
Other
Segment Reporting Information [Line Items]
Revenues before realized gains (losses)	58	90	194	284
Specialty Property and transportation | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net earned premiums	574	583	1,350	1,323
Specialty casualty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net earned premiums	560	658	1,663	1,921
Specialty financial | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net earned premiums	155	161	455	458
Other specialty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net earned premiums	50	40	132	113
Other lines | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net earned premiums	$ 42	$ 0	$ 174	$ 0