Investments - OTTI (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) securities	Sep. 30, 2018 USD ($) securities	Sep. 30, 2019 USD ($) securities	Sep. 30, 2018 USD ($) securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 3,000,000	$ 6,000,000	$ 22,000,000	$ 16,000,000
No. of Securities | securities	15	22	32	43
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Credit Impairments, Available-for-sale Securities	$ 1,000,000		$ 19,000,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Intent Impairments, Available-for-sale Securities	2		3
U.S. corporate public securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 0	$ 5,000,000	$ 0	$ 5,000,000
No. of Securities | securities	0	2	0	2
Foreign corporate public securities and foreign governments
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 1,000,000	$ 0	$ 2,000,000	$ 0
No. of Securities | securities	2	0	3	0
Foreign corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 0	$ 0	$ 18,000,000	$ 9,000,000
No. of Securities | securities	1	0	4	1
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 2,000,000	$ 1,000,000	$ 2,000,000	$ 2,000,000
No. of Securities | securities	11	20	21	40
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 0	$ 0	$ 0	$ 0
No. of Securities | securities	1	0	4	0