Fair Value Measurements - Changes in Unrealized Gains (Losses) Included in Net Income for Financial Instruments Classified at Fair Value (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended	5 Months Ended	6 Months Ended
	Jun. 30, 2018	May 31, 2018	Jun. 30, 2017	May 31, 2018	Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 7	$ (61)	$ (22)	$ (65)	$ (81)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0	0	0	1
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	8	43	39	82	136
Fair Value, Inputs, Level 3 [Member] | Other Policyholder Funds and Benefits Payable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	8	43	39	82	136
Fair Value, Inputs, Level 3 [Member] | Guaranteed Minimum Withdrawal Benefit [Member] | Other Policyholder Funds and Benefits Payable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	8	43	40	82	140
Fair Value, Inputs, Level 3 [Member] | Equity Linked Notes [Member] | Other Policyholder Funds and Benefits Payable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0	(1)	0	(4)
Fair Value, Inputs, Level 3 [Member] | Reinsurance Recoverable Including Reinsurance Premium Paid [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(1)	(11)	(7)	(19)	(23)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)	8	(52)	(3)	(48)	(47)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Interest Rate Contract [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	1	0	(5)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | US GMWB Hedging Instruments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	(15)	(5)	(17)	(41)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | US Macro Hedge Program [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)	8	(38)	2	(26)	(6)
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				2	(12)
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member] | Fixed Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	2	(12)
Available-for-sale Securities [Member] | Corporate | Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				$ 2	$ (12)
Available-for-sale Securities [Member] | Corporate | Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member] | Fixed Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 0	$ 2	$ (12)