Investments - Unrealized Capital Losses (Details) $ in Millions	Dec. 31, 2019 USD ($) securities	Dec. 31, 2018 USD ($) securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 1,389	$ 9,733
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	17	359
More Than Twelve Months Below Amortized Cost, Fair Value	1,043	2,392
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	46	201
Total Fair Value	2,432	12,125
Total Unrealized Capital Losses	$ 63	$ 560
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	567,000,000	2,444
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions | securities	289,000,000	1,894
More than twelve months below amortized cost, Number of Securities | securities	278,000,000	550
U.S. Treasuries
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 68	$ 0
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	3	0
More Than Twelve Months Below Amortized Cost, Fair Value	12	15
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	0	0
Total Fair Value	80	15
Total Unrealized Capital Losses	3	0
U.S. Government agencies and authorities
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Fair Value	18
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	0
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position More than Twelve Months, Fair Value	0
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position More than Twelve Months Accumulated Loss	0
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position, Fair Value	18
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position, Accumulated Loss	0
State, municipalities and political subdivisions
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	21	191
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	0	3
More Than Twelve Months Below Amortized Cost, Fair Value	0	88
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	0	5
Total Fair Value	21	279
Total Unrealized Capital Losses	0	8
U.S. corporate public securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	97	3,060
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	3	131
More Than Twelve Months Below Amortized Cost, Fair Value	131	535
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	10	50
Total Fair Value	228	3,595
Total Unrealized Capital Losses	13	181
U.S. corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	75	1,502
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	0	40
More Than Twelve Months Below Amortized Cost, Fair Value	134	579
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	16	66
Total Fair Value	209	2,081
Total Unrealized Capital Losses	16	106
Foreign corporate public securities and foreign governments
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	6	1,159
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	0	54
More Than Twelve Months Below Amortized Cost, Fair Value	53	169
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	3	26
Total Fair Value	59	1,328
Total Unrealized Capital Losses	3	80
Foreign corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	21	1,504
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	0	77
More Than Twelve Months Below Amortized Cost, Fair Value	56	221
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	1	20
Total Fair Value	77	1,725
Total Unrealized Capital Losses	1	97
Residential mortgage-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	535	560
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	6	11
More Than Twelve Months Below Amortized Cost, Fair Value	139	412
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	5	21
Total Fair Value	674	972
Total Unrealized Capital Losses	11	32
Commercial mortgage-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	331	865
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	3	16
More Than Twelve Months Below Amortized Cost, Fair Value	18	312
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	0	12
Total Fair Value	349	1,177
Total Unrealized Capital Losses	3	28
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	217	892
Available-for-sale Securities, Including Securities Pledged, Continuous Unrealized Loss Position Twelve Months or Less, Accumulated Loss	2	27
More Than Twelve Months Below Amortized Cost, Fair Value	500	61
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	11	1
Total Fair Value	717	953
Total Unrealized Capital Losses	13	$ 28
Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Unrealized Capital Losses	$ 7
More than twelve months below amortized cost, Number of Securities | securities	5