Derivative Financial Instruments - Schedule of Outstanding Hedges: (Notional Amount) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Derivatives not designated as hedging instruments | Interest-rate contracts | Swap agreements and forwards
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	$ 0	$ 336
Derivatives not designated as hedging instruments | Interest-rate contracts | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	6,492	2,621
Derivatives not designated as hedging instruments | Foreign exchange contracts | Futures
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	37	0
Derivatives not designated as hedging instruments | Foreign exchange contracts | Forward, swap and spot
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	1,313,515	1,274,277
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	131	403
Derivatives not designated as hedging instruments | Foreign exchange contracts | Options written
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	24	404
Derivatives not designated as hedging instruments | Credit derivative contracts | Credit swap agreements
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	0	141
Derivatives not designated as hedging instruments | Futures Contracts | Commodity
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	142	113
Derivatives not designated as hedging instruments | Futures Contracts | Equity
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	76	87
Derivatives not designated as hedging instruments | Other contracts | Stable value contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	27,319	24,583
Derivatives not designated as hedging instruments | Other contracts | Deferred value awards
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	456	320
Derivatives designated as hedging instruments | Interest-rate contracts | Swap agreements
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	10,276	9,398
Derivatives designated as hedging instruments | Foreign exchange contracts | Forward and swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	$ 4,812	$ 4,515