Derivative Financial Instruments - Volume and Fair Value Positions of Derivative Instruments (Details) $ in Millions	Mar. 31, 2019 USD ($) contract	Dec. 31, 2018 USD ($) contract
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 267	$ 292
Total liability derivatives, Notional amount	2,179	2,107
Total derivatives, Notional amount	$ 2,446	$ 2,399
Total asset derivatives, Number of contracts | contract	3,191	3,796
Total liability derivatives, Number of contracts | contract	3,097	3,266
Total derivatives, Number of contracts | contract	6,288	7,062
Total asset derivatives	$ 76	$ 28
Total liability derivatives	(265)	(227)
Total derivatives, Fair value, net	(189)	(199)
Asset derivatives, Gross asset	79	30
Asset derivatives, Gross liability	(3)	(2)
Liability derivatives, Gross asset	1	1
Liability derivatives, Gross liability	(266)	$ (228)
Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Number of contracts | contract		330
Interest rate cap agreements | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	4	$ 6
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	32	31
Total liability derivatives	1	1
Liability derivatives, Gross asset	1	1
Liability derivatives, Gross liability	0	0
Futures | Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount		0
Total asset derivatives		0
Asset derivatives, Gross asset		0
Asset derivatives, Gross liability		0
Futures | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 0
Total liability derivatives, Number of contracts | contract	80
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
Total asset derivatives, Number of contracts | contract		3,440
Total asset derivatives		$ 21
Asset derivatives, Gross asset		21
Asset derivatives, Gross liability		0
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	3,162
Total asset derivatives	$ 69
Asset derivatives, Gross asset	69
Asset derivatives, Gross liability	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	3,017	3,266
Total liability derivatives	$ (18)	$ (5)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(18)	(5)
Futures | 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	29	26
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	211	240
Total asset derivatives	7	8
Asset derivatives, Gross asset	8	8
Asset derivatives, Gross liability	(1)	0
Credit default swaps – buying protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	30	27
Total asset derivatives	0	0
Asset derivatives, Gross asset	2	1
Asset derivatives, Gross liability	(2)	(1)
Credit default swaps – buying protection | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	51
Total liability derivatives	(1)
Liability derivatives, Gross asset	0
Liability derivatives, Gross liability	(1)
Credit default swaps – selling protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	4
Total asset derivatives	0
Asset derivatives, Gross asset	0
Asset derivatives, Gross liability	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	1
Total liability derivatives	0	0
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	0	0
Other | Derivatives designated as fair value accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount	3
Total asset derivatives	0
Asset derivatives, Gross asset	0
Asset derivatives, Gross liability	0
Other | Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount		2
Total asset derivatives		0
Asset derivatives, Gross asset		0
Asset derivatives, Gross liability		0
Total return swap agreements - fixed income | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	3	7
Total asset derivatives	0	0
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	0
Total return swap agreements - equity | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	12	10
Total asset derivatives	0	(1)
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	(1)
Guaranteed accumulation benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	179	169
Total liability derivatives	(19)	(25)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(19)	(25)
Guaranteed withdrawal benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	221	210
Total liability derivatives	(12)	(14)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(12)	(14)
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	1,695	1,696
Total liability derivatives	(216)	(184)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	$ (216)	$ (184)