Financial Derivatives (Derivative Assets and Liabilitites Offsetting) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Document Period End Date	Jun. 30, 2018
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	$ 1,892	$ 2,874
Derivative Asset, Fair Value Offset Amount	742	1,054
Derivative Asset, Cash Collateral	92	636
Derivative Asset, Net Fair Value	1,058	1,184
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	2,883	2,856
Derivative Liability, Fair Value Offset Amount	742	1,054
Derivative Liability, Cash Collateral	723	763
Derivative Liability, Net Fair Value	1,418	1,039
Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	2,883	2,856
Derivative Liability, Fair Value Offset Amount	742	1,054
Derivative Liability, Cash Collateral	723	763
Derivative Liability, Net Fair Value	1,418	1,039
Derivative Liability, Net	1,418	1,039
Assets [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	1,892	2,874
Derivative Asset, Fair Value Offset Amount	742	1,054
Derivative Asset, Cash Collateral	92	636
Derivative Asset, Net Fair Value	1,058	1,184
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	20	32
Derivative Asset, Net	1,038	1,152
Interest Rate Contracts [Member] | Liability [Member] | Over the Counter Cleared, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	12	260
Derivative Liability, Fair Value Offset Amount		251
Derivative Liability, Cash Collateral
Derivative Liability, Net Fair Value	12	9
Derivative Liability, Net	12	9
Interest Rate Contracts [Member] | Liability [Member] | Over The Counter, Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	1,966	1,703
Derivative Liability, Fair Value Offset Amount	591	662
Derivative Liability, Cash Collateral	482	669
Derivative Liability, Net Fair Value	893	372
Derivative Liability, Net	893	372
Interest Rate Contracts [Member] | Assets [Member] | Over the Counter Cleared [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	15	827
Derivative Asset, Fair Value Offset Amount		251
Derivative Asset, Cash Collateral		567
Derivative Asset, Net Fair Value	15	9
Derivative Asset, Net	15	9
Interest Rate Contracts [Member] | Assets [Member] | Exchange Traded [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	1
Derivative Asset, Net Fair Value	1
Derivative Asset, Net	1
Interest Rate Contracts [Member] | Assets [Member] | Over the Counter [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	1,261	1,695
Derivative Asset, Fair Value Offset Amount	467	668
Derivative Asset, Cash Collateral	81	67
Derivative Asset, Net Fair Value	713	960
Derivative Asset, Securities Collateral Held Under Master Netting Agreements	20	32
Derivative Asset, Net	693	928
Foreign Exchange And Other Contract [Member] | Liability [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Gross Fair Value	905	893
Derivative Liability, Fair Value Offset Amount	151	141
Derivative Liability, Cash Collateral	241	94
Derivative Liability, Net Fair Value	513	658
Derivative Liability, Net	513	658
Foreign Exchange And Other Contract [Member] | Assets [Member]
Offsetting Assets [Line Items]
Derivative Asset, Gross Fair Value	615	352
Derivative Asset, Fair Value Offset Amount	275	135
Derivative Asset, Cash Collateral	11	2
Derivative Asset, Net Fair Value	329	215
Derivative Asset, Net	$ 329	$ 215