Fair Value Measurements - Fair Value Measurement (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets:
Derivatives	$ 122	$ 128
Assets held in separate accounts	73,369	67,323
Liabilities:
Derivatives	182	99
U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	567	738
U.S. government agencies and authorities
Assets:
Fixed maturities, including securities pledged	0	0
State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	789	764
U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	7,972	8,015
U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	3,886	3,653
Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,636	2,540
Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,325	3,175
Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	3,245	3,036
Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,153	1,905
Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	1,329	1,208
Assets measured on recurring basis
Assets:
Fixed maturities, including securities pledged	25,902	25,034
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	1,400	1,207
Assets held in separate accounts	73,369	67,323
Total assets, fair value	$ 100,880	$ 93,749
Percentage of Level to total assets	100.00%	100.00%
Liabilities:
Total liabilities, fair value	$ 156	$ 34
Assets measured on recurring basis | FIA
Liabilities:
Product guarantees	11	11
Assets measured on recurring basis | Stabilizer and MCGs
Liabilities:
Product guarantees	4	4
Assets measured on recurring basis | Credit contracts
Liabilities:
Derivatives	2	2
Assets measured on recurring basis | Interest rate contracts
Assets:
Derivatives	113	117
Liabilities:
Derivatives	156	76
Assets measured on recurring basis | Foreign exchange contracts
Assets:
Derivatives	7	10
Liabilities:
Derivatives	22	20
Assets measured on recurring basis | Equity contract
Assets:
Derivatives	2	1
Liabilities:
Derivatives	2	1
Assets measured on recurring basis | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	(41)	(80)
Assets measured on recurring basis | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	567	738
Assets measured on recurring basis | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	789	764
Assets measured on recurring basis | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	7,972	8,015
Assets measured on recurring basis | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	3,886	3,653
Assets measured on recurring basis | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,636	2,540
Assets measured on recurring basis | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,325	3,175
Assets measured on recurring basis | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	3,245	3,036
Assets measured on recurring basis | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,153	1,905
Assets measured on recurring basis | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	1,329	1,208
Assets measured on recurring basis | Equity securities
Assets:
Equity securities	87	57
Assets measured on recurring basis | Level 1
Assets:
Fixed maturities, including securities pledged	506	679
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	1,400	1,207
Assets held in separate accounts	67,616	61,457
Total assets, fair value	$ 69,530	$ 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	506	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	24,203	23,316
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	0	0
Assets held in separate accounts	5,686	5,805
Total assets, fair value	$ 30,010	$ 29,249
Percentage of Level to total assets	30.00%	31.00%
Liabilities:
Total liabilities, fair value	$ 141	$ 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	112	117
Liabilities:
Derivatives	156	76
Assets measured on recurring basis | Level 2 | Foreign exchange contracts
Assets:
Derivatives	7	10
Liabilities:
Derivatives	22	20
Assets measured on recurring basis | Level 2 | Equity contract
Assets:
Derivatives	2	1
Liabilities:
Derivatives	2	1
Assets measured on recurring basis | Level 2 | Embedded derivative on reinsurance
Liabilities:
Embedded derivative on reinsurance	(41)	(80)
Assets measured on recurring basis | Level 2 | U.S. Treasuries
Assets:
Fixed maturities, including securities pledged	61	59
Assets measured on recurring basis | Level 2 | State, municipalities and political subdivisions
Assets:
Fixed maturities, including securities pledged	789	764
Assets measured on recurring basis | Level 2 | U.S. corporate public securities
Assets:
Fixed maturities, including securities pledged	7,920	7,987
Assets measured on recurring basis | Level 2 | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	2,998	2,882
Assets measured on recurring basis | Level 2 | Foreign corporate public securities and foreign governments
Assets:
Fixed maturities, including securities pledged	2,636	2,540
Assets measured on recurring basis | Level 2 | Foreign corporate private securities
Assets:
Fixed maturities, including securities pledged	3,203	3,051
Assets measured on recurring basis | Level 2 | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	3,214	3,026
Assets measured on recurring basis | Level 2 | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	2,142	1,893
Assets measured on recurring basis | Level 2 | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	1,240	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	1,193	1,039
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	0	0
Assets held in separate accounts	67	61
Total assets, fair value	$ 1,340	$ 1,150
Percentage of Level to total assets	1.00%	1.00%
Liabilities:
Total liabilities, fair value	$ 15	$ 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	4	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	52	28
Assets measured on recurring basis | Level 3 | U.S. corporate private securities
Assets:
Fixed maturities, including securities pledged	888	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	122	124
Assets measured on recurring basis | Level 3 | Residential mortgage-backed
Assets:
Fixed maturities, including securities pledged	31	10
Assets measured on recurring basis | Level 3 | Commercial mortgage-backed
Assets:
Fixed maturities, including securities pledged	11	12
Assets measured on recurring basis | Level 3 | Other asset-backed securities
Assets:
Fixed maturities, including securities pledged	89	94
Assets measured on recurring basis | Level 3 | Equity securities
Assets:
Equity securities	$ 80	$ 50