Fair Value Measurements - Fair Value Measurement (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Assets:
Derivatives	$ 215	$ 128
Assets held in separate accounts	75,592	67,323
Liabilities:
Derivatives	334	99
U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	576	738
State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	813	764
U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	8,070	8,015
U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	3,930	3,653
Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,696	2,540
Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,307	3,175
Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	3,617	3,036
Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,259	1,905
Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	1,432	1,208
Assets measured on recurring basis
Assets:
Fixed maturities, including securities pledged	26,700	25,034
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	1,415	1,207
Assets held in separate accounts	75,592	67,323
Total assets, fair value	$ 104,012	$ 93,749
Percentage of Level to total assets	100.00%	100.00%
Liabilities:
Total liabilities, fair value	$ 361	$ 34
Assets measured on recurring basis | FIA
Liabilities:
Product guarantees	11	11
Assets measured on recurring basis | Stabilizer and MCGs
Liabilities:
Product guarantees	19	4
Assets measured on recurring basis | Credit contracts
Liabilities:
Derivatives	2	2
Assets measured on recurring basis | Interest rate contracts
Assets:
Derivatives	197	117
Liabilities:
Derivatives	315	76
Assets measured on recurring basis | Foreign exchange contracts
Assets:
Derivatives	15	10
Liabilities:
Derivatives	15	20
Assets measured on recurring basis | Equity contract
Assets:
Derivatives	3	1
Liabilities:
Derivatives	2	1
Assets measured on recurring basis | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	(3)	(80)
Assets measured on recurring basis | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	576	738
Assets measured on recurring basis | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	813	764
Assets measured on recurring basis | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	8,070	8,015
Assets measured on recurring basis | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	3,930	3,653
Assets measured on recurring basis | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,696	2,540
Assets measured on recurring basis | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,307	3,175
Assets measured on recurring basis | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	3,617	3,036
Assets measured on recurring basis | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,259	1,905
Assets measured on recurring basis | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	1,432	1,208
Assets measured on recurring basis | Equity securities
Assets:
Equity securities	90	57
Assets measured on recurring basis | Level 1
Assets:
Fixed maturities, including securities pledged	512	679
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	1,415	1,207
Assets held in separate accounts	69,521	61,457
Total assets, fair value	$ 71,456	$ 63,350
Percentage of Level to total assets	69.00%	68.00%
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
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 1 | Interest rate contracts
Assets:
Derivatives	1	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	512	679
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	7	7
Assets measured on recurring basis | Level 2
Assets:
Fixed maturities, including securities pledged	24,998	23,316
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	0	0
Assets held in separate accounts	5,969	5,805
Total assets, fair value	$ 31,181	$ 29,249
Percentage of Level to total assets	30.00%	31.00%
Liabilities:
Total liabilities, fair value	$ 331	$ 19
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
Liabilities:
Derivatives	2	2
Assets measured on recurring basis | Level 2 | Interest rate contracts
Assets:
Derivatives	196	117
Liabilities:
Derivatives	315	76
Assets measured on recurring basis | Level 2 | Foreign exchange contracts
Assets:
Derivatives	15	10
Liabilities:
Derivatives	15	20
Assets measured on recurring basis | Level 2 | Equity contract
Assets:
Derivatives	3	1
Liabilities:
Derivatives	2	1
Assets measured on recurring basis | Level 2 | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	(3)	(80)
Assets measured on recurring basis | Level 2 | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	64	59
Assets measured on recurring basis | Level 2 | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	813	764
Assets measured on recurring basis | Level 2 | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	8,023	7,987
Assets measured on recurring basis | Level 2 | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	3,037	2,882
Assets measured on recurring basis | Level 2 | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,696	2,540
Assets measured on recurring basis | Level 2 | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,133	3,051
Assets measured on recurring basis | Level 2 | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	3,601	3,026
Assets measured on recurring basis | Level 2 | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,259	1,893
Assets measured on recurring basis | Level 2 | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	1,372	1,114
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	1,190	1,039
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	0	0
Assets held in separate accounts	102	61
Total assets, fair value	$ 1,375	$ 1,150
Percentage of Level to total assets	1.00%	1.00%
Liabilities:
Total liabilities, fair value	$ 30	$ 15
Assets measured on recurring basis | Level 3 | FIA
Liabilities:
Product guarantees	11	11
Assets measured on recurring basis | Level 3 | Stabilizer and MCGs
Liabilities:
Product guarantees	19	4
Assets measured on recurring basis | Level 3 | Credit contracts
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 | 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	47	28
Assets measured on recurring basis | Level 3 | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	893	771
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	174	124
Assets measured on recurring basis | Level 3 | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	16	10
Assets measured on recurring basis | Level 3 | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	0	12
Assets measured on recurring basis | Level 3 | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	60	94
Assets measured on recurring basis | Level 3 | Equity securities
Assets:
Equity securities	$ 83	$ 50