Derivative Financial Instruments (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) contract	Dec. 31, 2016 USD ($) contract
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Assumed recoveries under sale of credit protection	$ 0
Securities pledged in the form of margin deposits	18,000,000
Derivatives, Fair Value
Total asset derivatives, Notional amount	179,000,000	$ 395,000,000
Total liability derivatives, Notional amount	2,689,000,000	2,524,000,000
Total derivatives, Notional amount	$ 2,868,000,000	$ 2,919,000,000
Total asset derivatives, Number of contracts | contract	4,441	3,923
Total liability derivatives, Number of contracts | contract	4,041	3,928
Total derivatives, Number of contracts | contract	8,482	7,851
Total asset derivatives	$ 95,000,000	$ 101,000,000
Total liability derivatives	(330,000,000)	(329,000,000)
Total derivatives, Fair value, net	(235,000,000)	(228,000,000)
Asset derivatives, Gross asset	96,000,000	103,000,000
Asset derivatives, Gross liability	(1,000,000)	(2,000,000)
Liability derivatives, Gross asset	1,000,000	0
Liability derivatives, Gross liability	(331,000,000)	(329,000,000)
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 130,000,000	$ 346,000,000
Total asset derivatives, Number of contracts | contract	4,441	3,923
Total asset derivatives	$ 94,000,000	$ 96,000,000
Asset derivatives, Gross asset	94,000,000	98,000,000
Asset derivatives, Gross liability	0	(2,000,000)
Foreign currency swap agreements | Derivatives designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	49,000,000	49,000,000
Total asset derivatives	1,000,000	5,000,000
Asset derivatives, Gross asset	2,000,000	5,000,000
Asset derivatives, Gross liability	(1,000,000)	0
Interest rate cap agreements | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	41,000,000	65,000,000
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
Interest rate cap agreements | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	11,000,000
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	4,336	3,917
Total asset derivatives	$ 92,000,000	$ 87,000,000
Asset derivatives, Gross asset	92,000,000	87,000,000
Asset derivatives, Gross liability	0	0
Financial futures contracts | Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 0	$ 0
Total asset derivatives, Number of contracts | contract	105	6
Total asset derivatives	$ 0	$ 0
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	0
Foreign currency forwards | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	1,000,000	173,000,000
Total asset derivatives	0	7,000,000
Asset derivatives, Gross asset	0	8,000,000
Asset derivatives, Gross liability	0	(1,000,000)
Foreign currency forwards | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	177,000,000
Total liability derivatives	(4,000,000)
Liability derivatives, Gross asset	1,000,000
Liability derivatives, Gross liability	(5,000,000)
Credit default swaps – buying protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	4,000,000	25,000,000
Total asset derivatives	0	(1,000,000)
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	(1,000,000)
Credit default swaps – buying protection | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	70,000,000	6,000,000
Total liability derivatives	(2,000,000)	0
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(2,000,000)	0
Credit default swaps – selling protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	81,000,000	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		100,000,000
Total liability derivatives		(3,000,000)
Liability derivatives, Gross asset		0
Liability derivatives, Gross liability		(3,000,000)
Other contracts | 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	1,000,000
Asset derivatives, Gross asset	0	1,000,000
Asset derivatives, Gross liability	0	0
Options and futures | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 190,000,000	$ 0
Total liability derivatives, Number of contracts | contract	4,041	3,928
Total liability derivatives	$ (34,000,000)	$ (37,000,000)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(34,000,000)	(37,000,000)
Guaranteed accumulation benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	234,000,000	391,000,000
Total liability derivatives	(25,000,000)	(34,000,000)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(25,000,000)	(34,000,000)
Guaranteed withdrawal benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	274,000,000	290,000,000
Total liability derivatives	(14,000,000)	(9,000,000)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(14,000,000)	(9,000,000)
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	1,733,000,000	1,737,000,000
Total liability derivatives	(251,000,000)	(246,000,000)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	$ (251,000,000)	$ (246,000,000)