Financial Derivatives (Derivative Assets and Liabilitites Offsetting) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	$ 2,874	$ 4,616
Derivative Asset, Fair Value Offset Amount	1,054	2,460
Derivative Asset, Cash Collateral	636	657
Derivative Asset, Net Fair Value	1,184	1,499
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	2,856	3,839
Derivative Liability, Fair Value Offset Amount	1,054	2,460
Derivative Liability, Cash Collateral	763	484
Derivative Liability, Net Fair Value	1,039	895
Liability
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	2,856	3,839
Derivative Liability, Fair Value Offset Amount	1,054	2,460
Derivative Liability, Cash Collateral	763	484
Derivative Liability, Net Fair Value	1,039	895
Derivative Liability	1,039	895
Assets
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	2,874	4,616
Derivative Asset, Fair Value Offset Amount	1,054	2,460
Derivative Asset, Cash Collateral	636	657
Derivative Asset, Net Fair Value	1,184	1,499
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	32	62
Derivative Asset, Net	1,152	1,437
Interest Rate Contract | Liability | Exchange Cleared, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	260	1,060
Derivative Liability, Fair Value Offset Amount	251	940
Derivative Liability, Cash Collateral		25
Derivative Liability, Net Fair Value	9	95
Derivative Liability	9	95
Interest Rate Contract | Liability | Exchange Traded, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value		1
Derivative Liability, Net Fair Value		1
Derivative Liability		1
Interest Rate Contract | Liability | Over The Counter, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	1,703	2,064
Derivative Liability, Fair Value Offset Amount	662	1,395
Derivative Liability, Cash Collateral	669	431
Derivative Liability, Net Fair Value	372	238
Derivative Liability	372	238
Interest Rate Contract | Assets | Exchange Cleared
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	827	1,498
Derivative Asset, Fair Value Offset Amount	251	940
Derivative Asset, Cash Collateral	567	480
Derivative Asset, Net Fair Value	9	78
Derivative Asset, Net	9	78
Interest Rate Contract | Assets | Exchange Traded
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value		9
Derivative Asset, Net Fair Value		9
Derivative Asset, Net		9
Interest Rate Contract | Assets | Over the Counter
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	1,695	2,702
Derivative Asset, Fair Value Offset Amount	668	1,358
Derivative Asset, Cash Collateral	67	164
Derivative Asset, Net Fair Value	960	1,180
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	32	62
Derivative Asset, Net	928	1,118
Foreign Exchange And Other Contract | Liability
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	893	714
Derivative Liability, Fair Value Offset Amount	141	125
Derivative Liability, Cash Collateral	94	28
Derivative Liability, Net Fair Value	658	561
Derivative Liability	658	561
Foreign Exchange And Other Contract | Assets
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	352	407
Derivative Asset, Fair Value Offset Amount	135	162
Derivative Asset, Cash Collateral	2	13
Derivative Asset, Net Fair Value	215	232
Derivative Asset, Net	$ 215	$ 232