Derivative Financial Instruments - Schedule of Outstanding Hedges: (Notional Amount) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Derivatives not designated as hedging instruments | Interest rate contracts | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	$ 12,668	$ 8,683
Derivatives not designated as hedging instruments | Foreign exchange contracts | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	197	1,550
Derivatives not designated as hedging instruments | Foreign exchange contracts | Forward, swap and spot
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	2,528,115	2,267,221
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	851	607
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options written
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	544	445
Derivatives not designated as hedging instruments | Other derivative contracts | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	125	0
Derivatives not designated as hedging instruments | Other derivative contracts | Stable value contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	28,704	31,391
Derivatives not designated as hedging instruments | Other derivative contracts | Deferred value awards
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	289	300
Derivatives designated as hedging instruments | Interest rate contracts | Swap agreements
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	20,333	22,566
Derivatives designated as hedging instruments | Foreign exchange contracts | Forward and swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivative instruments	$ 9,777	$ 8,213