Derivative Financial Instruments - Schedule of Outstanding Hedges: (Notional Amount) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	$ 11,047	$ 10,169
Additional compensation and employee benefits expense due to accelerated vesting	249
Derivatives not designated as hedging instruments | Interest-rate contracts(6) | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	2,392	13,455
Derivatives not designated as hedging instruments | Foreign exchange contracts | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	50	0
Derivatives not designated as hedging instruments | Foreign exchange contracts | Forward, swap and spot
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	1,679,976	1,414,765
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	350	337
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options written
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	302	202
Derivatives not designated as hedging instruments | Commodity and Equity Contracts | Commodity
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	16	0
Derivatives not designated as hedging instruments | Commodity and Equity Contracts | Equity
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	50	0
Derivatives not designated as hedging instruments | Other contracts | Stable value contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	26,653	27,182
Derivatives not designated as hedging instruments | Other contracts | Deferred value awards
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	473	409
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	11,047	10,169
Derivatives designated as hedging instruments | Foreign exchange contracts | Forward and swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	$ 28,913	$ 8,564