Fair Value Measurements - Changes in Unrealized Gains (Losses) Included in Net Income for Financial Instruments Classified at Fair Value (Details) - USD ($) $ in Millions	3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	May 31, 2018	Sep. 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)	$ (104)	$ (12)	$ (100)	$ (65)	$ (94)
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)	45	58	53	82	193
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)	45	58	53	82	193
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)	45	58	53	82	197
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	0	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)	(9)	(9)	(10)	(19)	(33)
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)	(95)	(2)	(90)	(48)	(49)
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)	1	0	1	(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)	(14)	(16)	(14)	(17)	(57)
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)	(82)	14	(77)	(26)	8
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	(13)
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	(1)	0
Corporate | 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	$ (13)
Corporate | 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	$ (1)	$ 0