Investments - OTTI (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) securities	Jun. 30, 2018 USD ($) securities	Jun. 30, 2019 USD ($) securities	Jun. 30, 2018 USD ($) securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 1,000,000	$ 1,000,000	$ 19,000,000	$ 10,000,000
No. of Securities | securities	9	21	20	25
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Credit Impairments, Available-for-sale Securities	$ 0	$ 1,000,000	$ 18,000,000	$ 10,000,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Intent Impairments, Available-for-sale Securities	1	0	1	0
Foreign corporate public securities and foreign governments
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 1,000,000	$ 0	$ 1,000,000	$ 0
No. of Securities | securities	1	0	1	0
Foreign corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment			$ 18,000,000	$ 9,000,000
No. of Securities | securities			3	1
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 0	$ 1,000,000	$ 0	$ 1,000,000
No. of Securities | securities	7	21	13	24
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 0	$ 0	$ 0	$ 0
No. of Securities | securities	1	0	3	0