Derivative Financial Instruments and Off-balance sheet Financial Instruments - Summary of the volume and fair value positions (Details) $ in Millions	Dec. 31, 2020 USD ($) contract	Dec. 31, 2019 USD ($) contract
Derivatives, Fair Value
Total asset derivatives, notional amount	$ 2,009	$ 75
Total liability derivatives, notional amount	3,182	3,403
Total derivatives, notional amount	$ 5,191	$ 3,478
Total asset derivatives, number of contracts | contract	4,440	10,740
Total liability derivatives, number of contracts | contract	4,108	6,492
Total derivatives, number of contracts | contract	8,548	17,232
Net amount on balance sheet	$ 206	$ 142
Net amount on balance sheet	(655)	(507)
Total derivatives, fair value, net	(449)	(365)
Asset derivatives, gross asset	218	142
Liability derivatives, gross asset	2	39
Asset derivatives, gross liability	(12)	0
Liability derivatives, gross liability	(657)	(546)
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	$ 2,006	$ 73
Total asset derivatives, number of contracts | contract	4,440	10,740
Net amount on balance sheet	$ 206	$ 142
Asset derivatives, gross asset	218	142
Asset derivatives, gross liability	(12)	$ 0
Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
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
Other | Other assets | Derivatives designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	3	2
Net amount on balance sheet	0	0
Asset derivatives, gross asset	0	0
Asset derivatives, gross liability	0	0
Interest rate cap agreements | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	13
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	19	34
Net amount on balance sheet	0	0
Liability derivatives, gross asset	0	0
Liability derivatives, gross liability	$ 0	$ 0
Futures | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, number of contracts | contract	602	3,668
Net amount on balance sheet	$ 0	$ 0
Asset derivatives, gross asset	0	0
Asset derivatives, gross liability	$ 0	$ 0
Futures | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, number of contracts | contract	730
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, number of contracts | contract	2,887	5,539
Net amount on balance sheet	$ 190	$ 140
Asset derivatives, gross asset	190	140
Asset derivatives, gross liability	$ 0	$ 0
Options | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, number of contracts | contract	2,712	5,400
Net amount on balance sheet	$ (110)	$ (68)
Liability derivatives, gross asset	0	0
Liability derivatives, gross liability	$ (110)	$ (68)
Futures | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, number of contracts | contract	951	1,533
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, number of contracts | contract	666	3
Net amount on balance sheet	$ 0	$ 0
Liability derivatives, gross asset	0	0
Liability derivatives, gross liability	0	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
Net amount on balance sheet		1
Asset derivatives, gross asset		1
Asset derivatives, gross liability		0
Total return swap agreements - fixed income | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	50	119
Net amount on balance sheet	0	0
Liability derivatives, gross asset	0	0
Liability derivatives, gross liability	0	0
Total return swap agreements - equity index | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	8
Net amount on balance sheet	1
Asset derivatives, gross asset	1
Asset derivatives, gross liability	0
Total return swap agreements - equity index | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount		187
Net amount on balance sheet		11
Liability derivatives, gross asset		11
Liability derivatives, gross liability		0
Foreign currency forwards | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	404
Net amount on balance sheet	5
Asset derivatives, gross asset	13
Asset derivatives, gross liability	(8)
Foreign currency forwards | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	367	745
Net amount on balance sheet	(13)	19
Liability derivatives, gross asset	2	28
Liability derivatives, gross liability	(15)	(9)
Embedded derivative financial instruments | Other investments
Derivatives, Fair Value
Total asset derivatives, notional amount	750
Net amount on balance sheet	0
Asset derivatives, gross asset	0
Asset derivatives, gross liability	0
Guaranteed accumulation benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	128	161
Net amount on balance sheet	(18)	(18)
Liability derivatives, gross asset	0	0
Liability derivatives, gross liability	(18)	(18)
Guaranteed withdrawal benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	190	205
Net amount on balance sheet	(15)	(14)
Liability derivatives, gross asset	0	0
Liability derivatives, gross liability	(15)	(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	1,785	1,791
Net amount on balance sheet	(483)	(430)
Liability derivatives, gross asset	0	0
Liability derivatives, gross liability	(483)	(430)
Credit default swaps – buying protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	77	17
Net amount on balance sheet	(4)	0
Asset derivatives, gross asset	0	0
Asset derivatives, gross liability	(4)	0
Credit default swaps – buying protection | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	638	152
Net amount on balance sheet	(16)	(7)
Liability derivatives, gross asset	0	0
Liability derivatives, gross liability	(16)	(7)
Credit default swaps – selling protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	754
Net amount on balance sheet	13
Asset derivatives, gross asset	13
Asset derivatives, gross liability	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	5	9
Net amount on balance sheet	0	0
Liability derivatives, gross asset	0	0
Liability derivatives, gross liability	$ 0	$ 0