Derivative Financial Instruments - Volume and Fair Value Positions of Derivative Instruments (Details) $ in Millions	Mar. 31, 2018 USD ($) contract	Dec. 31, 2017 USD ($) contract
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 112	$ 101
Total liability derivatives, Notional amount	2,455	2,525
Total derivatives, Notional amount	$ 2,567	$ 2,626
Total asset derivatives, Number of contracts | contract	4,220	4,485
Total liability derivatives, Number of contracts | contract	4,135	4,464
Total derivatives, Number of contracts | contract	8,355	8,949
Total asset derivatives	$ 84	$ 115
Total liability derivatives	(299)	(343)
Total derivatives, Fair value, net	(215)	(228)
Asset derivatives, Gross asset	84	115
Asset derivatives, Gross liability	0	0
Liability derivatives, Gross asset	4	3
Liability derivatives, Gross liability	(303)	(346)
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 2,436	$ 2,506
Total liability derivatives, Number of contracts | contract	4,135	4,464
Total liability derivatives	$ (301)	$ (345)
Liability derivatives, Gross asset	2	1
Liability derivatives, Gross liability	(303)	(346)
Foreign currency swap agreements | Derivatives designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	19	19
Total liability derivatives	2	2
Liability derivatives, Gross asset	2	2
Liability derivatives, Gross liability	0	0
Interest rate cap agreements | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	16	15
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	26	30
Total liability derivatives	1	1
Liability derivatives, Gross asset	1	1
Liability derivatives, Gross liability	0	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	4,136	4,485
Total asset derivatives	$ 84	$ 114
Asset derivatives, Gross asset	84	114
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
Total asset derivatives, Number of contracts | contract	84
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	11
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	148	207
Total liability derivatives	(7)	(8)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(7)	(8)
Credit default swaps – buying protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	2	3
Total asset derivatives	0	0
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	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	59	34
Total liability derivatives	(1)	(1)
Liability derivatives, Gross asset	1	0
Liability derivatives, Gross liability	(2)	(1)
Credit default swaps – selling protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	80	80
Total asset derivatives	0	1
Asset derivatives, Gross asset	0	1
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
Total liability derivatives		0
Liability derivatives, Gross asset		0
Liability derivatives, Gross liability		0
Other contracts | Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount	3	3
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	4,135	4,464
Total liability derivatives	$ (34)	$ (53)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(34)	(53)
Guaranteed accumulation benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	215	225
Total liability derivatives	(20)	(22)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(20)	(22)
Guaranteed withdrawal benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	266	274
Total liability derivatives	(10)	(12)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(10)	(12)
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	1,722	1,735
Total liability derivatives	(230)	(250)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	$ (230)	$ (250)