Fair Value Measurements - Fair Value Measurement (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets:
Derivatives	$ 148	$ 136
Assets held in separate accounts	73,489	73,036
Liabilities:
Derivatives	102	85
Fixed maturities
Assets:
Fixed maturities, including securities pledged	24,678	25,042
U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	552	656
U.S. government agencies and authorities
Assets:
Fixed maturities, including securities pledged	0	3
State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	859	878
U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	8,792	9,236
U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	3,395	3,497
Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,696	2,777
Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,276	3,215
Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,695	2,629
Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	1,567	1,470
Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	846	681
Equity securities
Assets:
Equity securities		60
Assets measured on recurring basis
Assets:
Fixed maturities, including securities pledged	24,678	25,042
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	1,010	1,078
Assets held in separate accounts	73,489	73,036
Total assets, fair value	$ 99,383	$ 99,352
Percentage of Level to total assets	100.00%	100.00%
Liabilities:
Total liabilities, fair value	$ 146	$ 181
Assets measured on recurring basis | FIA
Liabilities:
Product guarantees	18	20
Assets measured on recurring basis | Stabilizer and MCGs
Liabilities:
Product guarantees	77	97
Assets measured on recurring basis | Credit contracts
Assets:
Derivatives	8	10
Liabilities:
Derivatives	4	6
Assets measured on recurring basis | Interest rate contracts
Assets:
Derivatives	133	117
Liabilities:
Derivatives	16	20
Assets measured on recurring basis | Foreign exchange contracts
Assets:
Derivatives	1	0
Liabilities:
Derivatives	77	52
Assets measured on recurring basis | Equity contract
Assets:
Derivatives	6	9
Liabilities:
Derivatives	5	7
Assets measured on recurring basis | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	(51)	(21)
Assets measured on recurring basis | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	552	656
Assets measured on recurring basis | U.S. government agencies and authorities
Assets:
Fixed maturities, including securities pledged	0	3
Assets measured on recurring basis | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	859	878
Assets measured on recurring basis | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	8,792	9,236
Assets measured on recurring basis | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	3,395	3,497
Assets measured on recurring basis | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,696	2,777
Assets measured on recurring basis | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,276	3,215
Assets measured on recurring basis | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,695	2,629
Assets measured on recurring basis | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	1,567	1,470
Assets measured on recurring basis | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	846	681
Assets measured on recurring basis | Equity securities
Assets:
Equity securities	58	60
Assets measured on recurring basis | Level 1
Assets:
Fixed maturities, including securities pledged	494	597
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	1,010	1,078
Assets held in separate accounts	68,387	67,966
Total assets, fair value	$ 69,901	$ 69,651
Percentage of Level to total assets	70.00%	70.00%
Liabilities:
Total liabilities, fair value	$ 0	$ 0
Assets measured on recurring basis | Level 1 | FIA
Liabilities:
Product guarantees	0	0
Assets measured on recurring basis | Level 1 | Stabilizer and MCGs
Liabilities:
Product guarantees	0	0
Assets measured on recurring basis | Level 1 | Credit contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 1 | Interest rate contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 1 | Foreign exchange contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 1 | Equity contract
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 1 | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	0	0
Assets measured on recurring basis | Level 1 | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	494	597
Assets measured on recurring basis | Level 1 | U.S. government agencies and authorities
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 1 | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 1 | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 1 | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 1 | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 1 | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 1 | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 1 | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 1 | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 1 | Equity securities
Assets:
Equity securities	10	10
Assets measured on recurring basis | Level 2
Assets:
Fixed maturities, including securities pledged	23,218	23,614
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	0	0
Assets held in separate accounts	5,091	5,059
Total assets, fair value	$ 28,457	$ 28,809
Percentage of Level to total assets	29.00%	29.00%
Liabilities:
Total liabilities, fair value	$ 51	$ 64
Assets measured on recurring basis | Level 2 | FIA
Liabilities:
Product guarantees	0	0
Assets measured on recurring basis | Level 2 | Stabilizer and MCGs
Liabilities:
Product guarantees	0	0
Assets measured on recurring basis | Level 2 | Credit contracts
Assets:
Derivatives	8	10
Liabilities:
Derivatives	4	6
Assets measured on recurring basis | Level 2 | Interest rate contracts
Assets:
Derivatives	133	117
Liabilities:
Derivatives	16	20
Assets measured on recurring basis | Level 2 | Foreign exchange contracts
Assets:
Derivatives	1	0
Liabilities:
Derivatives	77	52
Assets measured on recurring basis | Level 2 | Equity contract
Assets:
Derivatives	6	9
Liabilities:
Derivatives	5	7
Assets measured on recurring basis | Level 2 | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	(51)	(21)
Assets measured on recurring basis | Level 2 | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	58	59
Assets measured on recurring basis | Level 2 | U.S. government agencies and authorities
Assets:
Fixed maturities, including securities pledged	0	3
Assets measured on recurring basis | Level 2 | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	859	878
Assets measured on recurring basis | Level 2 | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	8,777	9,210
Assets measured on recurring basis | Level 2 | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	2,744	2,855
Assets measured on recurring basis | Level 2 | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,696	2,777
Assets measured on recurring basis | Level 2 | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,175	3,123
Assets measured on recurring basis | Level 2 | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,622	2,608
Assets measured on recurring basis | Level 2 | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	1,567	1,463
Assets measured on recurring basis | Level 2 | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	720	638
Assets measured on recurring basis | Level 2 | Equity securities
Assets:
Equity securities	0	0
Assets measured on recurring basis | Level 3
Assets:
Fixed maturities, including securities pledged	966	831
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	0	0
Assets held in separate accounts	11	11
Total assets, fair value	$ 1,025	$ 892
Percentage of Level to total assets	1.00%	1.00%
Liabilities:
Total liabilities, fair value	$ 95	$ 117
Assets measured on recurring basis | Level 3 | FIA
Liabilities:
Product guarantees	18	20
Assets measured on recurring basis | Level 3 | Stabilizer and MCGs
Liabilities:
Product guarantees	77	97
Assets measured on recurring basis | Level 3 | Credit contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 3 | Interest rate contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 3 | Foreign exchange contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 3 | Equity contract
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 3 | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	0	0
Assets measured on recurring basis | Level 3 | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 3 | U.S. government agencies and authorities
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 3 | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 3 | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	15	26
Assets measured on recurring basis | Level 3 | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	651	642
Assets measured on recurring basis | Level 3 | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 3 | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	101	92
Assets measured on recurring basis | Level 3 | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	73	21
Assets measured on recurring basis | Level 3 | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	0	7
Assets measured on recurring basis | Level 3 | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	126	43
Assets measured on recurring basis | Level 3 | Equity securities
Assets:
Equity securities	$ 48	$ 50