Financial Derivatives (Derivative Assets and Liabilitites Offsetting) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	$ 1,789	$ 2,874
Derivative Asset, Fair Value Offset Amount	710	1,054
Derivative Asset, Cash Collateral	80	636
Derivative Asset, Net Fair Value	999	1,184
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	2,942	2,856
Derivative Liability, Fair Value Offset Amount	710	1,054
Derivative Liability, Cash Collateral	728	763
Derivative Liability, Net Fair Value	1,504	1,039
Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	2,942	2,856
Derivative Liability, Fair Value Offset Amount	710	1,054
Derivative Liability, Cash Collateral	728	763
Derivative Liability, Net Fair Value	1,504	1,039
Derivative Liability, Net	1,504	1,039
Assets [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	1,789	2,874
Derivative Asset, Fair Value Offset Amount	710	1,054
Derivative Asset, Cash Collateral	80	636
Derivative Asset, Net Fair Value	999	1,184
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	19	32
Derivative Asset, Net	980	1,152
Interest Rate Contracts [Member] | Liability [Member] | Over the Counter Cleared, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	11	260
Derivative Liability, Fair Value Offset Amount		251
Derivative Liability, Cash Collateral
Derivative Liability, Net Fair Value	11	9
Derivative Liability, Net	11	9
Interest Rate Contracts [Member] | Liability [Member] | Over The Counter, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	2,029	1,703
Derivative Liability, Fair Value Offset Amount	563	662
Derivative Liability, Cash Collateral	435	669
Derivative Liability, Net Fair Value	1,031	372
Derivative Liability, Net	1,031	372
Interest Rate Contracts [Member] | Assets [Member] | Over the Counter Cleared [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	16	827
Derivative Asset, Fair Value Offset Amount		251
Derivative Asset, Cash Collateral		567
Derivative Asset, Net Fair Value	16	9
Derivative Asset, Net	16	9
Interest Rate Contracts [Member] | Assets [Member] | Over the Counter [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	1,138	1,695
Derivative Asset, Fair Value Offset Amount	432	668
Derivative Asset, Cash Collateral	75	67
Derivative Asset, Net Fair Value	631	960
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	19	32
Derivative Asset, Net	612	928
Foreign Exchange And Other Contract [Member] | Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	902	893
Derivative Liability, Fair Value Offset Amount	147	141
Derivative Liability, Cash Collateral	293	94
Derivative Liability, Net Fair Value	462	658
Derivative Liability, Net	462	658
Foreign Exchange And Other Contract [Member] | Assets [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	635	352
Derivative Asset, Fair Value Offset Amount	278	135
Derivative Asset, Cash Collateral	5	2
Derivative Asset, Net Fair Value	352	215
Derivative Asset, Net	$ 352	$ 215