Derivative Financial Instruments - Summary of the volume and fair value positions of derivative instruments (Details) $ in Millions	Mar. 31, 2020 USD ($) contract	Dec. 31, 2019 USD ($) contract	Mar. 31, 2019 contract
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash and securities pledged in the form of margin deposits	$ 39
Derivatives, Fair Value
Total asset derivatives, notional amount	835	$ 75
Total liability derivatives, notional amount	3,051	3,403
Total derivatives, notional amount	$ 3,886	$ 3,478
Total asset derivatives, number of contracts | contract	3,842	10,740
Total liability derivatives, number of contracts | contract	11,300	6,492
Total derivatives, Number of contracts | contract	15,142	17,232
Derivative assets net amount on balance sheet	$ 59	$ 142
Asset derivatives gross amount	69	142
Asset derivatives, gross liability	(10)	0
Derivative liabilities net amount on balance sheet	(421)	(507)
Total derivatives, fair value, net	(362)	(365)
Liability derivatives, gross asset	8	39
Liability derivatives gross amount	(429)	(546)
Derivatives designated as fair value accounting hedging instruments
Derivatives, Fair Value
Total derivatives, Number of contracts | contract			1
Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	$ 833	$ 73
Total asset derivatives, number of contracts | contract	3,842	10,740
Derivative assets net amount on balance sheet	$ 59	$ 142
Asset derivatives gross amount	69	142
Asset derivatives, gross liability	$ (10)	$ 0
Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, number of contracts | contract	568	3,668
Currency Swap | Other investments | Derivatives designated as fair value accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount		$ 2
Derivative assets net amount on balance sheet		0
Asset derivatives gross amount		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	$ 33	34
Derivative liabilities net amount on balance sheet	0	0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	0	0
Futures | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	0	0
Derivative assets net amount on balance sheet	0	0
Asset derivatives gross amount	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, notional amount	$ 0	$ 0
Total liability derivatives, number of contracts | contract	6,808	1,089
Derivative liabilities net amount on balance sheet	$ (1)	$ 0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(1)	0
Equity and index contracts | 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	3,016	5,400
Derivative liabilities net amount on balance sheet	$ (4)	$ (68)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(4)	(68)
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	3,262	5,539
Derivative assets net amount on balance sheet	$ 21	$ 140
Asset derivatives gross amount	21	140
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	12	1,533
Derivative assets net amount on balance sheet	$ 0	$ 1
Asset derivatives gross amount	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	$ 0
Total liability derivatives, number of contracts | contract	1,476	3
Derivative liabilities net amount on balance sheet	$ (2)	$ 0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(2)	0
Total return swap agreements – fixed income | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	83	56
Derivative assets net amount on balance sheet	(5)	1
Asset derivatives gross amount	0	1
Asset derivatives, gross liability	(5)	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	2	119
Derivative liabilities net amount on balance sheet	0	0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	0	0
Total return swap agreements – equity index | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	6
Derivative liabilities net amount on balance sheet	(1)
Liability derivatives, gross asset	0
Liability derivatives gross amount	(1)
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
Derivative liabilities net amount on balance sheet		11
Liability derivatives, gross asset		11
Liability derivatives gross amount		0
Foreign currency forwards | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	629
Derivative assets net amount on balance sheet	42
Asset derivatives gross amount	44
Asset derivatives, gross liability	(2)
Foreign currency forwards | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	145	745
Derivative liabilities net amount on balance sheet	6	19
Liability derivatives, gross asset	7	28
Liability derivatives gross amount	(1)	(9)
Guaranteed accumulation benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	127	161
Derivative liabilities net amount on balance sheet	(33)	(18)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(33)	(18)
Guaranteed withdrawal benefits | Contractholder funds | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	164	205
Derivative liabilities net amount on balance sheet	(23)	(14)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(23)	(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	1,768	1,791
Derivative liabilities net amount on balance sheet	(361)	(430)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(361)	(430)
Credit default swaps – buying protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	114	17
Derivative assets net amount on balance sheet	1	0
Asset derivatives gross amount	4	0
Asset derivatives, gross liability	(3)	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	54	152
Derivative liabilities net amount on balance sheet	0	(7)
Liability derivatives, gross asset	1	0
Liability derivatives gross amount	(1)	(7)
Credit default swaps – selling protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	7
Derivative assets net amount on balance sheet	0
Asset derivatives gross amount	0
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	752	9
Derivative liabilities net amount on balance sheet	(2)	0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(2)	$ 0
Other | Other assets | Derivatives designated as fair value accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	2
Derivative assets net amount on balance sheet	0
Asset derivatives gross amount	0
Asset derivatives, gross liability	$ 0