Derivative Financial Instruments - Schedule of Outstanding Hedges: (Notional Amount) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		$ 11,025	$ 11,047
Derivatives not designated as hedging instruments | Interest-rate contracts(6) | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		1,942	2,392
Derivatives not designated as hedging instruments | Foreign exchange contracts | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		2	50
Derivatives not designated as hedging instruments | Foreign exchange contracts | Forward, swap and spot
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		2,219,600	1,679,976
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		778	350
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options written
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		553	302
Derivatives not designated as hedging instruments | Commodity and Equity Contracts | Commodity
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		13	16
Derivatives not designated as hedging instruments | Commodity and Equity Contracts | Equity
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		33	50
Derivatives not designated as hedging instruments | Other contracts | Stable value contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		25,881	26,653
Derivatives not designated as hedging instruments | Other contracts | Deferred value awards
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		619	473
Additional compensation and employee benefits expense due to accelerated vesting	$ 249
Derivatives designated as hedging instruments | Interest-rate contracts(6) | Swap agreements
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		11,025	11,047
Derivatives designated as hedging instruments | Foreign exchange contracts | Forward and swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives		$ 10,231	$ 28,913