Derivative Financial Instruments - Volume and Fair Value Positions of Derivative Instruments (Details) $ in Millions	Jun. 30, 2019 USD ($) contract	Dec. 31, 2018 USD ($) contract	Jun. 30, 2018 contract
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 18	$ 292
Total liability derivatives, Notional amount	2,350	2,107
Total derivatives, Notional amount	$ 2,368	$ 2,399
Total asset derivatives, Number of contracts | contract	3,520	3,796
Total liability derivatives, Number of contracts | contract	3,010	3,266
Total derivatives, Number of contracts | contract	6,530	7,062
Total asset derivatives, Fair value, net	$ 85	$ 28
Total liability derivatives, Fair value, net	(432)	(227)
Total derivatives, Fair value, net	(347)	(199)
Asset derivatives, Gross asset	85	30
Asset derivatives, Gross liability	0	(2)
Liability derivatives, Gross asset	9	1
Liability derivatives, Gross liability	$ (441)	(228)
Derivatives designated as fair value accounting hedging instruments
Derivatives, Fair Value
Total derivatives, Number of contracts | contract	1		1
Other | Derivatives designated as fair value accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 2
Total asset derivatives, Fair value, net	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, Fair value, net		0
Asset derivatives, Gross asset		0
Asset 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		6
Total asset derivatives, Fair value, net		0
Asset derivatives, Gross asset		0
Asset derivatives, Gross liability		0
Interest rate cap agreements | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	35	31
Total liability derivatives, Fair value, net	0	1
Liability derivatives, Gross asset	0	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	$ 0
Total asset derivatives, Number of contracts | contract	260	330
Total asset derivatives, Fair value, net	$ 0	$ 0
Asset derivatives, Gross asset	0	0
Asset 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	3,153	3,440
Total asset derivatives, Fair value, net	$ 84	$ 21
Asset derivatives, Gross asset	84	21
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	3,009	3,266
Total liability derivatives, Fair value, net	$ (28)	$ (5)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(28)	(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	107	26
Total asset derivatives, Fair value, net	$ 0	$ 0
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	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	1
Total liability derivatives, Fair value, net	$ 0
Liability derivatives, Gross asset	0
Liability 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, Fair value, net	0	0
Asset derivatives, Gross asset	0	0
Asset derivatives, Gross liability	0	0
Total return swap agreements - fixed income | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	13
Total liability derivatives, Fair value, net	1
Liability derivatives, Gross asset	1
Liability derivatives, Gross liability	0
Total return swap agreements - equity index | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	12	10
Total asset derivatives, Fair value, net	1	(1)
Asset derivatives, Gross asset	1	0
Asset derivatives, Gross liability	0	(1)
Foreign currency forwards | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount		240
Total asset derivatives, Fair value, net		8
Asset derivatives, Gross asset		8
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	194
Total liability derivatives, Fair value, net	8
Liability derivatives, Gross asset	8
Liability derivatives, Gross liability	0
Credit default swaps – buying protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	1	27
Total asset derivatives, Fair value, net	0	0
Asset derivatives, Gross asset	0	1
Asset derivatives, Gross liability	0	(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	32
Total liability derivatives, Fair value, net	(2)
Liability derivatives, Gross asset	0
Liability derivatives, Gross liability	(2)
Guaranteed accumulation benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	172	169
Total liability derivatives, Fair value, net	(22)	(25)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(22)	(25)
Credit default swaps – selling protection | Derivatives not designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	5	1
Total liability derivatives, Fair value, net	0	0
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	0	0
Guaranteed withdrawal benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	209	210
Total liability derivatives, Fair value, net	(14)	(14)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(14)	(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	1,690	1,696
Total liability derivatives, Fair value, net	(375)	(184)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	$ (375)	$ (184)