Fair Value Measurements - Level 3 Financial Instruments (Details) - Level 3 - Assets measured on recurring basis - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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	$ 38	$ 3	$ 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	23	4	50	10
Issuances	0	0	0	0
Sales	0	0	0	(3)
Settlements	0	0	0	0
Transfers in to Level 3	0	0	0	2
Transfers out of Level 3	(5)	(1)	(5)	(9)
Fair Value, assets, ending balance	56	6	56	6
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	(63)	(141)	(97)	(151)
Total Realized/Unrealized Gains (Losses) Included in Net Income	24	8	58	20
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	0	0
Purchases	0	0	0	0
Issues	(1)	(1)	(2)	(3)
Sales	0	0	0	0
Settlements	(1)	0	0	0
Transfers in to Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, Derivatives, ending balance	(41)	(134)	(41)	(134)
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	(16)	(23)	(20)	(23)
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	(1)	(2)	(2)
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	1	8	2
Transfers in to Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, Derivatives, ending balance	(13)	(23)	(13)	(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	18	27	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	0	0	3	11
Issuances	0	0	0	0
Sales	0	0	(5)	0
Settlements	0	0	0	0
Transfers in to Level 3	0	0	0	9
Transfers out of Level 3	0	0	(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	738	595	642	525
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	0	0
Total Realized/Unrealized Gains (Losses) Included in OCI	(7)	1	(29)	6
Purchases	62	2	165	46
Issuances	0	0	0	0
Sales	0	(1)	(5)	(1)
Settlements	(5)	(10)	(9)	(10)
Transfers in to Level 3	60	12	84	43
Transfers out of Level 3	(8)	0	(8)	(10)
Fair Value, assets, ending balance	840	599	840	599
Change in Unrealized Gains (Losses) Included in Earnings	0	0	0	0
Foreign corporate public securities and foreign governments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	0		0
Total Realized/Unrealized Gains (Losses) Included in Net Income	0		0
Total Realized/Unrealized Gains (Losses) Included in OCI	0		0
Purchases	10		10
Issuances	0		0
Sales	0		0
Settlements	0		0
Transfers in to Level 3	0		0
Transfers out of Level 3	0		0
Fair Value, assets, ending balance	10		10
Change in Unrealized Gains (Losses) Included in Earnings	0		0
Foreign corporate private securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	122	128	92	154
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	(8)	0
Total Realized/Unrealized Gains (Losses) Included in OCI	(4)	(1)	17	(2)
Purchases	8	14	86	32
Issuances	0	0	0	0
Sales	0	0	(56)	0
Settlements	(9)	0	(10)	(10)
Transfers in to Level 3	4	0	0	0
Transfers out of Level 3	0	0	0	(33)
Fair Value, assets, ending balance	121	141	121	141
Change in Unrealized Gains (Losses) Included in Earnings	0	0	(8)	0
Residential mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	33	37	21	21
Total Realized/Unrealized Gains (Losses) Included in Net Income	(2)	(2)	(5)	(5)
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	0	0
Purchases	20	9	71	9
Issuances	0	0	0	0
Sales	0	0	(40)	0
Settlements	0	0	0	0
Transfers in to Level 3	0	0	0	2
Transfers out of Level 3	(9)	(17)	(5)	0
Fair Value, assets, ending balance	42	27	42	27
Change in Unrealized Gains (Losses) Included in Earnings	(2)	(2)	(5)	(5)
Commercial mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	16	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	13	8	13	8
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	(16)	(6)	(7)	(10)
Fair Value, assets, ending balance	13	8	13	8
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	97	36	43	27
Total Realized/Unrealized Gains (Losses) Included in Net Income	0	0	0	0
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	(2)	1
Purchases	11	32	43	33
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(1)	0	(3)	(2)
Transfers in to Level 3	0	0	21	0
Transfers out of Level 3	(26)	(24)	(21)	(15)
Fair Value, assets, ending balance	81	44	81	44
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	1,024	829	831	744
Total Realized/Unrealized Gains (Losses) Included in Net Income	(2)	(2)	(13)	(5)
Total Realized/Unrealized Gains (Losses) Included in OCI	(11)	0	(14)	5
Purchases	124	65	391	139
Issuances	0	0	0	0
Sales	0	(1)	(106)	(1)
Settlements	(15)	(10)	(22)	(22)
Transfers in to Level 3	64	12	105	54
Transfers out of Level 3	(59)	(47)	(47)	(68)
Fair Value, assets, ending balance	1,125	846	1,125	846
Change in Unrealized Gains (Losses) Included in Earnings	(2)	(2)	(13)	(5)
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, assets, beginning balance	53	51	50	48
Total Realized/Unrealized Gains (Losses) Included in Net Income	(1)	0	(1)	0
Total Realized/Unrealized Gains (Losses) Included in OCI	0	0	0	1
Purchases	0	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	52	51	52	51
Change in Unrealized Gains (Losses) Included in Earnings	(1)	0	(1)	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	1	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	0	0	1	0
Issuances	0	0	0	0
Sales	(1)	0	(1)	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	0	0	0	0
Change in Unrealized Gains (Losses) Included in Earnings	$ 0	$ 0	$ 0	$ 0