Derivative Financial Instruments - Volume and Fair Value Positions of Derivative Instruments (Details)	Jun. 30, 2018 USD ($) contract	Dec. 31, 2017 USD ($) contract
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 89,000,000	$ 101,000,000
Total liability derivatives, Notional amount	2,426,000,000	2,525,000,000
Total derivatives, Notional amount	$ 2,515,000,000	$ 2,626,000,000
Total asset derivatives, Number of contracts | contract	32,691	4,485
Total liability derivatives, Number of contracts | contract	33,098	4,464
Total derivatives, Number of contracts | contract	65,789	8,949
Total asset derivatives	$ 85,000,000	$ 115,000,000
Total liability derivatives	(283,000,000)	(343,000,000)
Total derivatives, Fair value, net	(198,000,000)	(228,000,000)
Asset derivatives, Gross asset	86,000,000	115,000,000
Asset derivatives, Gross liability	(1,000,000)	0
Liability derivatives, Gross asset	3,000,000	3,000,000
Liability derivatives, Gross liability	(286,000,000)	(346,000,000)
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount		$ 2,506,000,000
Total liability derivatives, Number of contracts | contract		4,464
Total liability derivatives		$ (345,000,000)
Liability derivatives, Gross asset		1,000,000
Liability derivatives, Gross liability		(346,000,000)
Foreign currency swap agreements | Derivatives designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount		19,000,000
Total liability derivatives		2,000,000
Liability derivatives, Gross asset		2,000,000
Liability derivatives, Gross liability		0
Interest rate cap agreements | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	13,000,000	15,000,000
Total asset derivatives	0	0
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	0
Interest rate cap agreements | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	28,000,000	30,000,000
Total liability derivatives	1,000,000	1,000,000
Liability derivatives, Gross asset	1,000,000	1,000,000
Liability derivatives, Gross liability	0	0
Financial options | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 0
Total asset derivatives, Number of contracts | contract	18
Total asset derivatives	$ 0
Asset derivatives, Gross asset	0
Asset derivatives, Gross liability	0
Financial options | Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 0
Total liability derivatives, Number of contracts | contract	574
Total liability derivatives	$ 0
Liability derivatives, Gross asset	0
Liability derivatives, Gross liability	0
Options | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 0	$ 0
Total asset derivatives, Number of contracts | contract	32,622	4,485
Total asset derivatives	$ 85,000,000	$ 114,000,000
Asset derivatives, Gross asset	85,000,000	114,000,000
Asset derivatives, Gross liability	0	0
Financial futures | Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 0
Total asset derivatives, Number of contracts | contract	51
Total asset derivatives	$ 0
Asset derivatives, Gross asset	0
Asset derivatives, Gross liability	0
Foreign currency forwards | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	9,000,000
Total asset derivatives	0
Asset derivatives, Gross asset	0
Asset derivatives, Gross liability	0
Foreign currency forwards | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	186,000,000	207,000,000
Total liability derivatives	1,000,000	(8,000,000)
Liability derivatives, Gross asset	2,000,000	0
Liability derivatives, Gross liability	(1,000,000)	(8,000,000)
Credit default swaps – buying protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	15,000,000	3,000,000
Total asset derivatives	(1,000,000)	0
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	(1,000,000)	0
Credit default swaps – buying protection | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	12,000,000	34,000,000
Total liability derivatives	0	(1,000,000)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	0	(1,000,000)
Credit default swaps – selling protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	30,000,000	80,000,000
Total asset derivatives	1,000,000	1,000,000
Asset derivatives, Gross asset	1,000,000	1,000,000
Asset derivatives, Gross liability	0	0
Credit default swaps – selling protection | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	1,000,000	1,000,000
Total liability derivatives	0	0
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	0	0
Other | Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount	3,000,000	3,000,000
Total asset derivatives	0	0
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	0
Options | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 0	$ 0
Total liability derivatives, Number of contracts | contract	32,524	4,464
Total liability derivatives	$ (28,000,000)	$ (53,000,000)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(28,000,000)	(53,000,000)
Total return swap agreements - fixed income | Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount	19,000,000
Total asset derivatives	0
Asset derivatives, Gross asset	0
Asset derivatives, Gross liability	0
Total return swap agreements - equity | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total liability derivatives, Notional amount	21,000,000
Total liability derivatives	0
Liability derivatives, Gross asset	0
Liability derivatives, Gross liability	0
Guaranteed accumulation benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	205,000,000	225,000,000
Total liability derivatives	(19,000,000)	(22,000,000)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(19,000,000)	(22,000,000)
Guaranteed withdrawal benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	252,000,000	274,000,000
Total liability derivatives	(10,000,000)	(12,000,000)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(10,000,000)	(12,000,000)
Equity-indexed and forward starting options in life and annuity product contracts | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	1,718,000,000	1,735,000,000
Total liability derivatives	(228,000,000)	(250,000,000)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	$ (228,000,000)	$ (250,000,000)