Derivative Financial Instruments and Off-balance sheet Financial Instruments - Summary of the volume and fair value positions (Details) $ in Millions	Dec. 31, 2019 USD ($) contract	Dec. 31, 2018 USD ($) contract
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 75	$ 470
Total liability derivatives, Notional amount	3,403	2,675
Total derivatives, Notional amount	$ 3,478	$ 3,145
Total asset derivatives, Number of contracts | contract	10,740	13,914
Total liability derivatives, Number of contracts | contract	6,492	12,256
Total derivatives, Number of contracts | contract	17,232	26,170
Net amount on balance sheet	$ 142	$ 124
Asset derivatives, Gross asset	142	130
Asset derivatives, gross liability	0	(6)
Net amount on balance sheet	(507)	(269)
Total derivatives, Fair value, net	(365)	(145)
Liability derivatives, Gross asset	39	12
Liability derivatives, Gross liability	(546)	(281)
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 73
Total asset derivatives, Number of contracts | contract	10,740
Net amount on balance sheet	$ 142
Asset derivatives, Gross asset	142
Asset derivatives, gross liability	0
Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount		$ 0
Total liability derivatives, Number of contracts | contract		1,300
Net amount on balance sheet		$ (1)
Liability derivatives, Gross asset		0
Liability derivatives, Gross liability		(1)
Other | Other assets | Derivatives designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	2
Net amount on balance sheet	0
Asset derivatives, Gross asset	0
Asset derivatives, gross liability	0
Other | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount		2
Net amount on balance sheet		0
Asset derivatives, Gross asset		0
Asset derivatives, gross liability		0
Interest rate cap agreements | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount		6
Net amount on balance sheet		0
Asset derivatives, Gross asset		0
Asset derivatives, gross liability		0
Interest rate cap agreements | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	34	31
Net amount on balance sheet	0	1
Liability derivatives, Gross asset	0	1
Liability derivatives, Gross liability	0	0
Futures | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 0	$ 0
Total asset derivatives, Number of contracts | contract	3,668	1,330
Net amount on balance sheet	$ 0	$ 1
Asset derivatives, Gross asset	0	1
Asset derivatives, gross liability	0	0
Futures | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 0
Total liability derivatives, Number of contracts | contract	1,089
Net amount on balance sheet	$ 0
Liability derivatives, Gross asset	0
Liability derivatives, Gross liability	0
Options | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 0	$ 0
Total asset derivatives, Number of contracts | contract	5,539	11,131
Net amount on balance sheet	$ 140	$ 115
Asset derivatives, Gross asset	140	115
Asset derivatives, gross liability	0	0
Futures | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	$ 0	$ 0
Total asset derivatives, Number of contracts | contract	1,533	1,453
Net amount on balance sheet	$ 1	$ 1
Asset derivatives, Gross asset	1	1
Asset derivatives, gross liability	0	0
Futures | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 0
Total liability derivatives, Number of contracts | contract	3
Net amount on balance sheet	$ 0
Liability derivatives, Gross asset	0
Liability derivatives, Gross liability	0
Total return swap agreements - fixed income | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	56	7
Total liability derivatives, Notional amount	119	38
Net amount on balance sheet	1	0
Asset derivatives, Gross asset	1	0
Asset derivatives, gross liability	0	0
Net amount on balance sheet	0	(1)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	0	(1)
Total return swap agreements - equity index | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount		61
Total liability derivatives, Notional amount	187	71
Net amount on balance sheet		(2)
Asset derivatives, Gross asset		0
Asset derivatives, gross liability		(2)
Net amount on balance sheet	11	(4)
Liability derivatives, Gross asset	11	0
Liability derivatives, Gross liability	0	(4)
Options and futures | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	$ 0	$ 0
Total liability derivatives, Number of contracts | contract	5,400	10,956
Net amount on balance sheet	$ (68)	$ (50)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(68)	(50)
Foreign currency forwards | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount		258
Net amount on balance sheet		10
Asset derivatives, Gross asset		11
Asset derivatives, gross liability		(1)
Foreign currency forwards | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	745	341
Net amount on balance sheet	19	10
Liability derivatives, Gross asset	28	11
Liability derivatives, Gross liability	(9)	(1)
Guaranteed accumulation benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	161	169
Net amount on balance sheet	(18)	(25)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(18)	(25)
Guaranteed withdrawal benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	205	210
Net amount on balance sheet	(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 | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	1,791	1,770
Net amount on balance sheet	(430)	(185)
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(430)	(185)
Credit default swaps – buying protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, Notional amount	17	136
Net amount on balance sheet	0	(1)
Asset derivatives, Gross asset	0	2
Asset derivatives, gross liability	0	(3)
Credit default swaps – buying protection | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	152	40
Net amount on balance sheet	(7)	0
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	(7)	0
Credit default swaps – selling protection | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, Notional amount	9	5
Net amount on balance sheet	0	0
Liability derivatives, Gross asset	0	0
Liability derivatives, Gross liability	$ 0	$ 0