Fair Value Measurements - Fair Value Measurement (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Assets:
Derivatives	$ 719	$ 224
Assets held in separate accounts	66,562	78,713
Liabilities:
Derivatives	795	285
U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	799	691
US Treasury and Government
Assets:
Fixed maturities, including securities pledged	20	19
State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	808	815
U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	7,507	8,031
U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	3,811	4,066
Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,497	2,679
Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,068	3,375
Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	4,169	3,810
Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,453	2,500
Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	1,340	1,474
Assets measured on recurring basis
Assets:
Fixed maturities, including securities pledged	26,472	27,460
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	2,052	1,429
Assets held in separate accounts	66,562	78,713
Total assets, fair value	$ 95,878	$ 107,906
Percentage of Level to total assets	100.00%	100.00%
Liabilities:
Total liabilities, fair value	$ 997	$ 341
Assets measured on recurring basis | FIA
Liabilities:
Product guarantees	9	11
Assets measured on recurring basis | Stabilizer and MCGs
Liabilities:
Product guarantees	193	22
Assets measured on recurring basis | Interest rate contracts
Assets:
Derivatives	646	210
Liabilities:
Derivatives	793	261
Assets measured on recurring basis | Foreign exchange contracts
Assets:
Derivatives	72	10
Liabilities:
Derivatives	0	19
Assets measured on recurring basis | Equity contract
Assets:
Derivatives	1	4
Liabilities:
Derivatives	0	3
Assets measured on recurring basis | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	0	23
Assets measured on recurring basis | Credit contracts
Liabilities:
Derivatives	2	2
Assets measured on recurring basis | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	799	691
Assets measured on recurring basis | US Treasury and Government
Assets:
Fixed maturities, including securities pledged	20
Assets measured on recurring basis | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	808	815
Assets measured on recurring basis | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	7,507	8,031
Assets measured on recurring basis | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	3,811	4,066
Assets measured on recurring basis | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,497	2,679
Assets measured on recurring basis | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,068	3,375
Assets measured on recurring basis | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	4,169	3,810
Assets measured on recurring basis | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,453	2,500
Assets measured on recurring basis | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	1,340	1,474
Assets measured on recurring basis | Equity securities
Assets:
Equity securities	73	80
Assets measured on recurring basis | Level 1
Assets:
Fixed maturities, including securities pledged	625	536
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	2,052	1,429
Assets held in separate accounts	59,476	72,448
Total assets, fair value	$ 62,196	$ 74,431
Percentage of Level to total assets	65.00%	69.00%
Liabilities:
Total liabilities, fair value	$ 2	$ 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 | Interest rate contracts
Assets:
Derivatives	28	1
Liabilities:
Derivatives	2	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 | Credit contracts
Liabilities:
Derivatives	0	0
Assets measured on recurring basis | Level 1 | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	625	536
Assets measured on recurring basis | Level 1 | US Treasury and Government
Assets:
Fixed maturities, including securities pledged	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	15	17
Assets measured on recurring basis | Level 2
Assets:
Fixed maturities, including securities pledged	24,680	25,621
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	0	0
Assets held in separate accounts	6,945	6,150
Total assets, fair value	$ 32,316	$ 31,994
Percentage of Level to total assets	34.00%	30.00%
Liabilities:
Total liabilities, fair value	$ 793	$ 308
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 | Interest rate contracts
Assets:
Derivatives	618	209
Liabilities:
Derivatives	791	261
Assets measured on recurring basis | Level 2 | Foreign exchange contracts
Assets:
Derivatives	72	10
Liabilities:
Derivatives	0	19
Assets measured on recurring basis | Level 2 | Equity contract
Assets:
Derivatives	1	4
Liabilities:
Derivatives	0	3
Assets measured on recurring basis | Level 2 | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	0	23
Assets measured on recurring basis | Level 2 | Credit contracts
Liabilities:
Derivatives	2	2
Assets measured on recurring basis | Level 2 | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	174	155
Assets measured on recurring basis | Level 2 | US Treasury and Government
Assets:
Fixed maturities, including securities pledged	20
Assets measured on recurring basis | Level 2 | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	808	815
Assets measured on recurring basis | Level 2 | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	7,463	7,984
Assets measured on recurring basis | Level 2 | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	2,920	3,064
Assets measured on recurring basis | Level 2 | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,494	2,679
Assets measured on recurring basis | Level 2 | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	2,909	3,185
Assets measured on recurring basis | Level 2 | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	4,154	3,794
Assets measured on recurring basis | Level 2 | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,453	2,500
Assets measured on recurring basis | Level 2 | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	1,285	1,426
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	1,167	1,303
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	0	0
Assets held in separate accounts	141	115
Total assets, fair value	$ 1,366	$ 1,481
Percentage of Level to total assets	1.00%	1.00%
Liabilities:
Total liabilities, fair value	$ 202	$ 33
Assets measured on recurring basis | Level 3 | FIA
Liabilities:
Product guarantees	9	11
Assets measured on recurring basis | Level 3 | Stabilizer and MCGs
Liabilities:
Product guarantees	193	22
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 | Credit contracts
Liabilities:
Derivatives	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 | US Treasury and Government
Assets:
Fixed maturities, including securities pledged	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	44	47
Assets measured on recurring basis | Level 3 | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	891	1,002
Assets measured on recurring basis | Level 3 | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	3	0
Assets measured on recurring basis | Level 3 | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	159	190
Assets measured on recurring basis | Level 3 | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	15	16
Assets measured on recurring basis | Level 3 | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	0	0
Assets measured on recurring basis | Level 3 | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	55	48
Assets measured on recurring basis | Level 3 | Equity securities
Assets:
Equity securities	$ 58	$ 63