Investments (excluding Consolidated Investment Entities) - Unrealized Capital Losses (Details) $ in Millions	Jun. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 5,226	$ 1,823
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 333	$ 21
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	835	334
More than twelve months below amortized cost, Fair Value	$ 827	$ 1,450
More than twelve months below amortized cost, Unrealized Capital Loss	$ 84	$ 70
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	236	338
Total, Fair Value	$ 6,053	$ 3,273
Total Unrealized Capital Losses	$ 417	$ 91
Total number of securities in an unrealized loss position | security	1,071	672
U.S. Treasuries
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 0	$ 2
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 0	0
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	0
More than twelve months below amortized cost, Fair Value	$ 0	21
More than twelve months below amortized cost, Unrealized Capital Loss	$ 0	0
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	0
Total, Fair Value	$ 0	23
Total Unrealized Capital Losses	$ 0	0
Total number of securities in an unrealized loss position | security	0
State, municipalities and political subdivisions
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 33	25
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 1	0
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	10
More than twelve months below amortized cost, Fair Value	$ 1	1
More than twelve months below amortized cost, Unrealized Capital Loss	$ 0	0
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	1
Total, Fair Value	$ 34	26
Total Unrealized Capital Losses	$ 1	0
Total number of securities in an unrealized loss position | security	11
U.S. corporate public securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 686	122
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 39	3
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	111
More than twelve months below amortized cost, Fair Value	$ 45	199
More than twelve months below amortized cost, Unrealized Capital Loss	$ 8	16
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	11
Total, Fair Value	$ 731	321
Total Unrealized Capital Losses	$ 47	19
Total number of securities in an unrealized loss position | security	122
U.S. corporate private securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 373	113
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 12	1
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	31
More than twelve months below amortized cost, Fair Value	$ 129	195
More than twelve months below amortized cost, Unrealized Capital Loss	$ 30	20
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	10
Total, Fair Value	$ 502	308
Total Unrealized Capital Losses	$ 42	21
Total number of securities in an unrealized loss position | security	41
Foreign corporate public securities and foreign governments
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 183	15
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 13	0
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	38
More than twelve months below amortized cost, Fair Value	$ 31	103
More than twelve months below amortized cost, Unrealized Capital Loss	$ 3	6
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	6
Total, Fair Value	$ 214	118
Total Unrealized Capital Losses	$ 16	6
Total number of securities in an unrealized loss position | security	44
Foreign corporate private securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 442	36
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 37	0
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	32
More than twelve months below amortized cost, Fair Value	$ 65	78
More than twelve months below amortized cost, Unrealized Capital Loss	$ 3	2
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	6
Total, Fair Value	$ 507	114
Total Unrealized Capital Losses	$ 40	2
Total number of securities in an unrealized loss position | security	38
Residential mortgage-backed
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 884	730
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 34	8
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	161
More than twelve months below amortized cost, Fair Value	$ 166	194
More than twelve months below amortized cost, Unrealized Capital Loss	$ 10	6
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	79
Total, Fair Value	$ 1,050	924
Total Unrealized Capital Losses	$ 44	14
Total number of securities in an unrealized loss position | security	240
Commercial mortgage-backed securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 1,629	472
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 166	4
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	247
More than twelve months below amortized cost, Fair Value	$ 9	18
More than twelve months below amortized cost, Unrealized Capital Loss	$ 1	0
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	1
Total, Fair Value	$ 1,638	490
Total Unrealized Capital Losses	$ 167	4
Total number of securities in an unrealized loss position | security	248
Other asset-backed securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Twelve months or less below amortized cost, Fair Value	$ 996	308
Twelve months or less below amortized cost, Unrealized Capital Loss	$ 31	5
Twelve months or less below amortized cost, total number of securities in an unrealized loss position | security	205
More than twelve months below amortized cost, Fair Value	$ 381	641
More than twelve months below amortized cost, Unrealized Capital Loss	$ 29	20
More than twelve months below amortized cost, total number of securities in an unrealized loss position | security	122
Total, Fair Value	$ 1,377	949
Total Unrealized Capital Losses	$ 60	$ 25
Total number of securities in an unrealized loss position | security	327