Derivative Financial Instruments and Off-balance sheet Financial Instruments - Derivatives not designated as accounting hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	$ 38	$ 11	$ (18)
Realized capital gains and losses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	(46)	0	(24)
Life and annuity contract benefits
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	9	9	(7)
Interest credited to contractholder funds
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	41	18	22
Operating costs and expenses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	34	(16)	(9)
Interest rate contracts
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives			1
Interest rate contracts | Realized capital gains and losses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives			1
Interest rate contracts | Life and annuity contract benefits
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives			0
Interest rate contracts | Interest credited to contractholder funds
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives			0
Interest rate contracts | Operating costs and expenses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives			0
Equity and index contracts
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	60	25	(9)
Equity and index contracts | Realized capital gains and losses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	(15)	(12)	1
Equity and index contracts | Life and annuity contract benefits
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	0	0	0
Equity and index contracts | Interest credited to contractholder funds
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	47	18	(9)
Equity and index contracts | Operating costs and expenses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	28	19	(1)
Embedded derivative financial instruments
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	3	9	24
Embedded derivative financial instruments | Realized capital gains and losses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	0	0	0
Embedded derivative financial instruments | Life and annuity contract benefits
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	9	9	(7)
Embedded derivative financial instruments | Interest credited to contractholder funds
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	(6)	0	31
Embedded derivative financial instruments | Operating costs and expenses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	0	0	0
Foreign currency contracts
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	(21)	(18)	(32)
Foreign currency contracts | Realized capital gains and losses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	(27)	17	(24)
Foreign currency contracts | Life and annuity contract benefits
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	0	0	0
Foreign currency contracts | Interest credited to contractholder funds
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	0	0	0
Foreign currency contracts | Operating costs and expenses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	6	(35)	(8)
Credit default contracts
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	(4)	(5)	(2)
Credit default contracts | Realized capital gains and losses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	(4)	(5)	(2)
Credit default contracts | Life and annuity contract benefits
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	0	0	0
Credit default contracts | Interest credited to contractholder funds
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	0	0	0
Credit default contracts | Operating costs and expenses
Derivative Instruments, Gain (Loss)
Derivatives not designated as accounting hedging instruments, total gain (loss) recognized in net income on derivatives	$ 0	$ 0	$ 0