Derivative Financial Instruments and Off-balance sheet Financial Instruments - Volume and fair value positions of derivative instruments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) contract	Dec. 31, 2017 USD ($) contract
Derivatives, Fair Value
Assumed recoveries under sale of credit protection	$ 0
Securities pledged in the form of margin deposits	7
Total asset derivatives, Notional amount	292	$ 101
Total liability derivatives, Notional amount	2,107	2,525
Total derivatives, Notional amount	$ 2,399	$ 2,626
Total asset derivatives, Number of contracts | contract	3,796,000,000	4,485
Total liability derivatives, Number of contracts | contract	3,266,000,000	4,464
Total derivatives, Number of contracts | contract	7,062,000,000	8,949
Total asset derivatives, Fair value, net	$ 28	$ 115
Asset derivatives, Gross asset	30	115
Asset derivatives, Gross liability	(2)	0
Derivative liabilities net amount on balance sheet	(227)	(343)
Total derivatives, Fair value, net	(199)	(228)
Liability derivatives, Gross asset	1	3
Liability derivatives, Gross liability	(228)	(346)
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount		$ 2,506
Total liability derivatives, Number of contracts | contract		4,464
Derivative liabilities net amount on balance sheet		$ (345)
Liability derivatives, Gross asset		1
Liability derivatives, Gross liability		(346)
Foreign currency swap agreements | Derivatives designated as accounting hedging instruments | Other liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount		19
Derivative liabilities net amount on balance sheet		2
Liability derivatives, Gross asset		2
Liability 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		30
Derivative liabilities net amount on balance sheet		1
Liability derivatives, Gross asset		1
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	6	15
Total asset derivatives, Fair value, net	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	31
Derivative liabilities net amount on balance sheet	1
Liability derivatives, Gross asset	1
Liability derivatives, Gross liability	0
Interest Rate Financial Futures Contracts [Member] | 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	330,000,000
Total asset derivatives, Fair value, net	$ 0
Asset derivatives, Gross asset	0
Asset 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	3,440,000,000	4,485
Total asset derivatives, Fair value, net	$ 21	$ 114
Asset derivatives, Gross asset	21	114
Asset 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, Number of contracts | contract	26,000,000
Total asset derivatives, Fair value, net	$ 0
Asset derivatives, Gross asset	0
Asset derivatives, Gross liability	0
Total return swaps - fixed income | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	7
Total asset derivatives, Fair value, net	0
Asset derivatives, Gross asset	0
Asset derivatives, Gross liability	0
Total return swaps - equity | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	10
Total asset derivatives, Fair value, net	(1)
Asset derivatives, Gross asset	0
Asset derivatives, Gross liability	(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		207
Derivative liabilities net amount on balance sheet		(8)
Liability derivatives, Gross asset		0
Liability derivatives, Gross liability		(8)
Credit default swaps – buying protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount	27	3
Total asset derivatives, Fair value, net	0	0
Asset derivatives, Gross asset	1	0
Asset derivatives, Gross liability	(1)	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		34
Derivative liabilities net amount on balance sheet		(1)
Liability derivatives, Gross asset		0
Liability derivatives, Gross liability		0
Credit default swaps – selling protection | Derivatives not designated as accounting hedging instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, Notional amount		80
Total asset derivatives, Fair value, net		1
Asset derivatives, Gross asset		1
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
Derivative liabilities net amount on balance sheet	0	0
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	0	(1)
Other | Derivatives not designated as accounting hedging instruments | Other assets
Derivatives, Fair Value
Total asset derivatives, Notional amount	2	3
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 liabilities & accrued expenses
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 0	$ 0
Total liability derivatives, Number of contracts | contract	3,266,000,000	4,464
Derivative liabilities net amount on balance sheet	$ (5)	$ (53)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(5)	(53)
Guaranteed accumulation benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	169	225
Derivative liabilities net amount on balance sheet	(25)	(22)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(25)	(22)
Guaranteed withdrawal benefits | Derivatives not designated as accounting hedging instruments | Contractholder funds
Derivatives, Fair Value
Total liability derivatives, Notional amount	210	274
Derivative liabilities net amount on balance sheet	(14)	(12)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(14)	(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	1,696	1,735
Derivative liabilities net amount on balance sheet	(184)	(250)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	$ (184)	$ (250)