Segment Information - Non-insurance Revenue from Customers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Fee income	$ 1,301	$ 1,313	$ 1,168
Other Income	170	105	85
Revenue from Contract with Customer, Excluding Assessed Tax	1,404	1,418	1,253
Installment billing fees [Member] | Operating Segments | Property and Casualty, Commercial Insurance [Member]
Segment Reporting Information [Line Items]
Fee income	35	34	37
Installment billing fees [Member] | Operating Segments | Property and Casualty, Personal Insurance [Member]
Segment Reporting Information [Line Items]
Fee income	37	40	44
Insurance servicing fees [Member] | Operating Segments | Property and Casualty, Personal Insurance [Member]
Segment Reporting Information [Line Items]
Other Income	83	84	85
Administrative services fees [Member] | Operating Segments | Group Benefits
Segment Reporting Information [Line Items]
Fee income	180	175	91
Advisor, distribution and other management fees [Member] | Operating Segments | Mutual Fund [Member]
Segment Reporting Information [Line Items]
Fee income	911	947	897
Other fees [Member] | Operating Segments | Mutual Fund [Member]
Segment Reporting Information [Line Items]
Fee income	88	85	95
Investment management and other fees [Member] | Corporate
Segment Reporting Information [Line Items]
Fee income	50	32	4
Transition service fees [Member] | Corporate
Segment Reporting Information [Line Items]
Other Income	$ 20	$ 21	$ 0