Goodwill & Other Intangible Assets - Goodwill Carrying Value (Details)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 1,290,000,000	$ 1,290,000,000
Goodwill related to acquisitions	623,000,000	0
Ending balance	1,913,000,000	1,290,000,000	$ 1,290,000,000
Goodwill, Impairment Loss	$ 0	0	0
Number of Reporting Units	5
Operating Segments | Property and Casualty, Commercial Insurance [Member]
Goodwill [Roll Forward]
Beginning balance	$ 38,000,000	38,000,000
Goodwill related to acquisitions	623,000,000	0
Ending balance	661,000,000	38,000,000	38,000,000
Operating Segments | Property and Casualty, Personal Insurance [Member]
Goodwill [Roll Forward]
Beginning balance	119,000,000	119,000,000
Goodwill related to acquisitions	0	0
Ending balance	119,000,000	119,000,000	119,000,000
Operating Segments | Mutual Fund [Member]
Goodwill [Roll Forward]
Beginning balance	180,000,000	180,000,000
Goodwill related to acquisitions	0	0
Ending balance	180,000,000	180,000,000	180,000,000
Operating Segments | Group Benefits
Goodwill [Roll Forward]
Beginning balance	723,000,000	723,000,000
Goodwill related to acquisitions	0	0
Ending balance	723,000,000	723,000,000	723,000,000
Corporate
Goodwill [Roll Forward]
Beginning balance	230,000,000	230,000,000
Goodwill related to acquisitions	0	0
Ending balance	230,000,000	230,000,000	230,000,000
Corporate | Mutual Fund [Member]
Goodwill [Roll Forward]
Beginning balance	92,000,000	92,000,000
Ending balance	92,000,000	92,000,000	92,000,000
Corporate | Group Benefits
Goodwill [Roll Forward]
Beginning balance	138,000,000	138,000,000
Ending balance	$ 138,000,000	$ 138,000,000	$ 138,000,000