Segment Information - Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 4,254	$ 4,250
Net investment income	470	451
Realized Investment Gains (Losses)	163	(30)
Other revenues	53	20
Total revenues	4,940	4,691
Corporate
Segment Reporting Information [Line Items]
Earned premiums and fee income	13	2
Property and Casualty, Commercial Insurance Product Line [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	1,786	1,720
Property and Casualty, Commercial Insurance Product Line [Member] | Workers’ compensation
Segment Reporting Information [Line Items]
Earned premiums and fee income	825	818
Property and Casualty, Commercial Insurance Product Line [Member] | Liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	168	151
Property and Casualty, Commercial Insurance Product Line [Member] | Package business
Segment Reporting Information [Line Items]
Earned premiums and fee income	352	332
Property and Casualty, Commercial Insurance Product Line [Member] | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	157	149
Property and Casualty, Commercial Insurance Product Line [Member] | Professional liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	68	62
Property and Casualty, Commercial Insurance Product Line [Member] | Bond
Segment Reporting Information [Line Items]
Earned premiums and fee income	60	58
Property and Casualty, Commercial Insurance Product Line [Member] | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	156	150
Property and Casualty, Personal Insurance Product Line [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	808	869
Property and Casualty, Personal Insurance Product Line [Member] | AARP Members [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	722	758
Property and Casualty, Personal Insurance Product Line [Member] | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	561	607
Property and Casualty, Personal Insurance Product Line [Member] | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	247	262
Group Insurance Policies [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	1,409	1,401
Group Insurance Policies [Member] | Group disability
Segment Reporting Information [Line Items]
Earned premiums and fee income	704	677
Group Insurance Policies [Member] | Group life
Segment Reporting Information [Line Items]
Earned premiums and fee income	643	664
Group Insurance Policies [Member] | Other
Segment Reporting Information [Line Items]
Earned premiums and fee income	62	60
Mutual Fund [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	238	258
Mutual Fund [Member] | Third party retail customers [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	216	232
Mutual Fund [Member] | Talcott Resolution [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 22	$ 26