Financial Derivatives (Derivative Assets and Liabilitites Offsetting) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	$ 3,093	$ 4,616
Derivative Asset, Fair Value Offset Amount	1,373	2,460
Derivative Asset, Cash Collateral	397	657
Derivative Asset, Net Fair Value	1,323	1,499
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	2,608	3,839
Derivative Liability, Fair Value Offset Amount	1,373	2,460
Derivative Liability, Cash Collateral	691	484
Derivative Liability, Net Fair Value	544	895
Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	2,608	3,839
Derivative Liability, Fair Value Offset Amount	1,373	2,460
Derivative Liability, Cash Collateral	691	484
Derivative Liability, Net Fair Value	544	895
Derivative Liability, Net	544	895
Assets [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	3,093	4,616
Derivative Asset, Fair Value Offset Amount	1,373	2,460
Derivative Asset, Cash Collateral	397	657
Derivative Asset, Net Fair Value	1,323	1,499
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	65	62
Derivative Asset, Net	1,258	1,437
Interest Rate Contracts [Member] | Liability [Member] | Exchange Cleared, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	196	1,060
Derivative Liability, Fair Value Offset Amount	177	940
Derivative Liability, Cash Collateral		25
Derivative Liability, Net Fair Value	19	95
Derivative Liability, Net	19	95
Interest Rate Contracts [Member] | Liability [Member] | Exchange Traded, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value		1
Derivative Liability, Net Fair Value		1
Derivative Liability, Net		1
Interest Rate Contracts [Member] | Liability [Member] | Over The Counter, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	1,804	2,064
Derivative Liability, Fair Value Offset Amount	1,027	1,395
Derivative Liability, Cash Collateral	590	431
Derivative Liability, Net Fair Value	187	238
Derivative Liability, Net	187	238
Interest Rate Contracts [Member] | Assets [Member] | Exchange Cleared [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	472	1,498
Derivative Asset, Fair Value Offset Amount	177	940
Derivative Asset, Cash Collateral	261	480
Derivative Asset, Net Fair Value	34	78
Derivative Asset, Net	34	78
Interest Rate Contracts [Member] | Assets [Member] | Exchange Traded [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	3	9
Derivative Asset, Net Fair Value	3	9
Derivative Asset, Net	3	9
Interest Rate Contracts [Member] | Assets [Member] | Over the Counter [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	2,362	2,702
Derivative Asset, Fair Value Offset Amount	1,080	1,358
Derivative Asset, Cash Collateral	133	164
Derivative Asset, Net Fair Value	1,149	1,180
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	65	62
Derivative Asset, Net	1,084	1,118
Foreign Exchange And Other Contract [Member] | Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	608	714
Derivative Liability, Fair Value Offset Amount	169	125
Derivative Liability, Cash Collateral	101	28
Derivative Liability, Net Fair Value	338	561
Derivative Liability, Net	338	561
Foreign Exchange And Other Contract [Member] | Assets [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	256	407
Derivative Asset, Fair Value Offset Amount	116	162
Derivative Asset, Cash Collateral	3	13
Derivative Asset, Net Fair Value	137	232
Derivative Asset, Net	$ 137	$ 232