Fair Value Measurements - Other Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	$ 148	$ 136
Short-term loan affiliate	0	80
Other investments	22	0
Assets held in separate accounts	73,489	73,036
Derivatives liabilities	102	85
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, including securities pledged	24,678	25,042
Equity securities	58	60
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	1,010	1,078
Derivative assets	148	136
Notes receivable from affiliates	175	175
Short-term loan affiliate	0	80
Other investments	22	0
Assets held in separate accounts	73,489	73,036
Deposit liabilities	77	135
Derivatives liabilities	102	85
Long-term debt, fair value	4	5
Carrying Value | Embedded derivative on reinsurance
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Embedded derivative on reinsurance	(51)	(21)
Carrying Value | Funding agreements without fixed maturities and deferred annuities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	25,599	25,314
Carrying Value | Funding agreements with fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	225	0
Carrying Value | Supplementary contracts, immediate annuities and other
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	357	365
Carrying Value | FIA
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	18	20
Carrying Value | Stabilizer and MCGs
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	77	97
Carrying Value | Mortgage loans on real estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	4,891	4,910
Carrying Value | Policy loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	212	214
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, including securities pledged	24,678	25,042
Equity securities	58	60
Cash and cash equivalents, short-term investments and short-term investments under securities loan agreement	1,010	1,078
Derivative assets	148	136
Notes receivable from affiliates	215	222
Short-term loan affiliate	0	80
Other investments	22	0
Assets held in separate accounts	73,489	73,036
Deposit liabilities	122	198
Derivatives liabilities	102	85
Long-term debt, fair value	4	5
Fair Value | Embedded derivative on reinsurance
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Embedded derivative on reinsurance	(51)	(21)
Fair Value | Funding agreements without fixed maturities and deferred annuities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	28,720	29,431
Fair Value | Funding agreements with fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	230	0
Fair Value | Supplementary contracts, immediate annuities and other
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	403	418
Fair Value | FIA
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	18	20
Fair Value | Stabilizer and MCGs
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities	77	97
Fair Value | Mortgage loans on real estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	4,885	4,924
Fair Value | Policy loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	$ 212	$ 214