Segment Information - Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 4,711	$ 4,254
Net investment income	459	470
Realized Investment Gains (Losses)	(231)	163
Other revenues	17	53
Total revenues	4,956	4,940
Corporate
Segment Reporting Information [Line Items]
Earned premiums and fee income	17	13
Property and Casualty, Commercial Insurance [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	2,273	1,786
Property and Casualty, Commercial Insurance [Member] | Workers’ compensation
Segment Reporting Information [Line Items]
Earned premiums and fee income	816	825
Property and Casualty, Commercial Insurance [Member] | Liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	343	168
Property and Casualty, Commercial Insurance [Member] | Marine
Segment Reporting Information [Line Items]
Earned premiums and fee income	65	0
Property and Casualty, Commercial Insurance [Member] | Package business
Segment Reporting Information [Line Items]
Earned premiums and fee income	377	352
Property and Casualty, Commercial Insurance [Member] | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	205	156
Property and Casualty, Commercial Insurance [Member] | Professional liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	143	68
Property and Casualty, Commercial Insurance [Member] | Bond
Segment Reporting Information [Line Items]
Earned premiums and fee income	70	60
Property and Casualty, Commercial Insurance [Member] | Assumed reinsurance
Segment Reporting Information [Line Items]
Earned premiums and fee income	66	0
Property and Casualty, Commercial Insurance [Member] | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	188	157
Property and Casualty, Personal Insurance [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	783	808
Property and Casualty, Personal Insurance [Member] | AARP Members [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	707	722
Property and Casualty, Personal Insurance [Member] | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	240	247
Property and Casualty, Personal Insurance [Member] | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	543	561
Group Insurance Policy [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	1,391	1,409
Group Insurance Policy [Member] | Group disability
Segment Reporting Information [Line Items]
Earned premiums and fee income	726	704
Group Insurance Policy [Member] | Group life
Segment Reporting Information [Line Items]
Earned premiums and fee income	607	643
Group Insurance Policy [Member] | Other
Segment Reporting Information [Line Items]
Earned premiums and fee income	58	62
Mutual Fund [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	247	238
Mutual Fund [Member] | Third party retail customers [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	225	216
Mutual Fund [Member] | Talcott Resolution [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 22	$ 22