Derivative Financial Instruments - Schedule of Outstanding Hedges: (Notional Amount) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Additional compensation and employee benefits expense due to accelerated vesting	$ 249
Derivatives not designated as hedging instruments | Interest-rate contracts(7) | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	13,455	$ 16,893
Derivatives not designated as hedging instruments | Foreign exchange contracts | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	0	3
Derivatives not designated as hedging instruments | Foreign exchange contracts | Forward, swap and spot
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	1,414,765	1,588,100
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	337	666
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options written
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	202	353
Derivatives not designated as hedging instruments | Other contracts | Stable value contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	27,182	26,020
Derivatives not designated as hedging instruments | Other contracts | Deferred value awards
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	409	652
Derivatives designated as hedging instruments | Interest-rate contracts(7) | Swap agreements
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	10,169	10,131
Derivatives designated as hedging instruments | Foreign exchange contracts | Forward and swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	$ 8,564	$ 12,735