Derivative Financial Instruments - Summary of the volume and fair value positions of derivative instruments (Details) $ in Millions	Mar. 31, 2022 USD ($) contract	Dec. 31, 2021 USD ($) contract
Derivatives, Fair Value
Total asset derivatives, notional amount	$ 1,241	$ 1,285
Total liability derivatives, notional amount	904	790
Total derivatives, notional amount	$ 2,145	$ 2,075
Total asset derivatives, number of contracts | contract	2,808	1,355
Total liability derivatives, number of contracts | contract	49,011	37,928
Total derivatives, Number of contracts | contract	51,819	39,283
Net amount on balance sheet	$ 93	$ 76
Net amount on balance sheet	(19)	9
Total derivatives, fair value, net	74	85
Asset derivatives gross amount	96	77
Liability derivatives, gross asset	19	23
Asset derivatives, gross liability	(3)	(1)
Liability derivatives gross amount	$ (38)	$ (14)
Futures | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, number of contracts | contract	660	1,181
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, number of contracts | contract	47,803	36,668
Net amount on balance sheet	$ (10)	$ (2)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	$ (10)	$ (2)
Options | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, number of contracts | contract	73	61
Net amount on balance sheet	$ 4	$ 5
Asset derivatives gross amount	4	5
Asset 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	2,075	113
Net amount on balance sheet	$ 4	$ 0
Asset derivatives gross amount	4	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	1,208	1,260
Net amount on balance sheet	$ (3)	$ (1)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(3)	(1)
Foreign currency forwards | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	194	2
Net amount on balance sheet	10	0
Asset derivatives gross amount	11	0
Asset derivatives, gross liability	(1)	0
Foreign currency forwards | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	506	715
Net amount on balance sheet	14	16
Liability derivatives, gross asset	19	23
Liability derivatives gross amount	(5)	(7)
Embedded derivative financial instruments | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	750	750
Net amount on balance sheet	0	0
Asset derivatives gross amount	0	0
Asset derivatives, gross liability	0	0
Contingent consideration | Other assets | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	250	250
Net amount on balance sheet	77	65
Asset derivatives gross amount	77	65
Asset derivatives, gross liability	0	0
Credit default swaps – buying protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount	47	33
Net amount on balance sheet	(2)	(1)
Asset derivatives gross amount	0	0
Asset derivatives, gross liability	(2)	(1)
Credit default swaps – buying protection | Other liabilities & accrued expenses | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total liability derivatives, notional amount	393	70
Net amount on balance sheet	(20)	(4)
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	(20)	(4)
Credit default swaps – selling protection | Other investments | Derivatives not designated as accounting hedging instruments
Derivatives, Fair Value
Total asset derivatives, notional amount		250
Net amount on balance sheet		6
Asset derivatives gross amount		6
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	5
Net amount on balance sheet	0	0
Liability derivatives, gross asset	0	0
Liability derivatives gross amount	$ 0	$ 0