Fair Value Measurements - Level 3 Financial Instruments (Details) - Level 3 - Assets measured on recurring basis - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Assets held in separate accounts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	$ 11	$ 13	$ 11	$ 6
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	0	0
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	0	0
Purchases	27	1	27	6
Issuances	0	0	0	0
Sales	0	(3)	0	(3)
Settlements	0	0	0	0
Transfers in to Level 3	0	0	0	2
Transfers out of Level 3	0	(8)	0	(8)
Fair Value, assets, ending balance	38	3	38	3
Change in Unrealized Gains (Losses) Included in Earnings	0	0	0	0
Stabilizer (Investment Only) and MCG Contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Derivatives, beginning balance	(77)	(131)	(97)	(151)
Total Realized/Unrealized Gains (Losses) Included in Net Income	13	(9)	34	12
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	0	0
Purchases	0	0	0	0
Issues	0	(1)	(1)	(2)
Sales	0	0	0	0
Settlements	1	0	1	0
Transfers in to Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, Derivatives, ending balance	(63)	(141)	(63)	(141)
Change In Unrealized Gains (Losses) Included in Earnings	0	0	0	0
FIA
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Derivatives, beginning balance	(18)	(23)	(20)	(23)
Total Realized/Unrealized Gains (Losses) Included in Net Income	(1)	0	(2)	(1)
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	0	0
Purchases	0	0	0	0
Issues	0	0	1	0
Sales	0	0	0	0
Settlements	3	0	5	1
Transfers in to Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, Derivatives, ending balance	(16)	(23)	(16)	(23)
Change In Unrealized Gains (Losses) Included in Earnings	0	0	0	0
U.S. corporate public securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	15	30	26	7
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	0	0
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	0	0
Purchases	3	6	3	11
Issuances	0	0	0	0
Sales	0	0	(5)	0
Settlements	0	1	0	0
Transfers in to Level 3	0	0	0	9
Transfers out of Level 3	0	(10)	(6)	0
Fair Value, assets, ending balance	18	27	18	27
Change in Unrealized Gains (Losses) Included in Earnings	0	0	0	0
U.S. corporate private securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	651	565	642	525
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	0	0
Total Realized/Unrealized Gains (Losses) Included in OCI	(3)	4	(18)	4
Purchases	91	8	103	45
Issuances	0	0	0	0
Sales	(5)	0	(5)	0
Settlements	(8)	(1)	(4)	(2)
Transfers in to Level 3	12	28	20	32
Transfers out of Level 3	0	(9)	0	(9)
Fair Value, assets, ending balance	738	595	738	595
Change in Unrealized Gains (Losses) Included in Earnings	0	0	0	0
Foreign corporate private securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	101	161	92	154
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	(9)	0
Total Realized/Unrealized Gains (Losses) Included in OCI	2	0	20	(1)
Purchases	75	0	75	18
Issuances	0	0	0	0
Sales	(56)	0	(56)	0
Settlements	0	0	0	(10)
Transfers in to Level 3	0	0	0	0
Transfers out of Level 3	0	(33)	0	(33)
Fair Value, assets, ending balance	122	128	122	128
Change in Unrealized Gains (Losses) Included in Earnings	0	0	(9)	0
Residential mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	73	30	21	21
Total Realized/Unrealized Gains (Losses) Included in Net Income	(1)	(2)	(3)	(3)
Total Realized/Unrealized Gains (Losses) Included in OCI	(1)	1	0	0
Purchases	19	17	20	17
Issuances	0	0	0	0
Sales	(40)	0	0	0
Settlements	0	0	0	0
Transfers in to Level 3	0	1	0	2
Transfers out of Level 3	(17)	(10)	(5)	0
Fair Value, assets, ending balance	33	37	33	37
Change in Unrealized Gains (Losses) Included in Earnings	2	(2)	(3)	(4)
Commercial mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	0	6	7	10
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	0	0
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	0	0
Purchases	16	2	16	2
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	(2)	0	(3)
Transfers in to Level 3	0	0	0	0
Transfers out of Level 3	0	0	(7)	(3)
Fair Value, assets, ending balance	16	6	16	6
Change in Unrealized Gains (Losses) Included in Earnings	0	0	0	0
Other asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	126	23	43	27
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	0	0
Total Realized/Unrealized Gains (Losses) Included in OCI	(1)	0	(2)	1
Purchases	57	24	57	24
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(1)	0	(2)	(1)
Transfers in to Level 3	21	0	22	0
Transfers out of Level 3	(105)	(11)	(21)	(15)
Fair Value, assets, ending balance	97	36	97	36
Change in Unrealized Gains (Losses) Included in Earnings	0	0	0	0
Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	966	815	831	744
Total Realized/Unrealized Gains (Losses) Included in Net Income	(1)	(2)	(12)	(3)
Total Realized/Unrealized Gains (Losses) Included in OCI	(3)	5	0	4
Purchases	261	57	274	117
Issuances	0	0	0	0
Sales	(101)	0	(66)	0
Settlements	(9)	(2)	(6)	(16)
Transfers in to Level 3	33	29	42	43
Transfers out of Level 3	(122)	(73)	(39)	(60)
Fair Value, assets, ending balance	1,024	829	1,024	829
Change in Unrealized Gains (Losses) Included in Earnings	2	(2)	(12)	(4)
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	48	50	50	48
Total Realized/Unrealized Gains (Losses) Included in Net Income	2	0	0	0
Total Realized/Unrealized Gains (Losses) Included in OCI	0	1	0	1
Purchases	3	0	3	2
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Transfers in to Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, assets, ending balance	53	51	53	51
Change in Unrealized Gains (Losses) Included in Earnings	2	0	0	0
Short-term investments and cash equivalents
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	0	0	0	0
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	0	0
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	0	0
Purchases	1	0	1	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Transfers in to Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, assets, ending balance	1	0	1	0
Change in Unrealized Gains (Losses) Included in Earnings	$ 0	$ 0	$ 0	$ 0