Derivative Financial Instruments - Fair Value Hedging Basis Adjusments (Details) - Fair Value Hedges - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
AFS securities | Hedged Items Currently Designated
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount	$ 350	$ 391
Hedge Basis Adjustment	58	69
AFS securities | Hedged Items No Longer Designated
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount	138	142
Hedge Basis Adjustment	5	5
Loans and leases | Hedged Items Currently Designated
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount	392	500
Hedge Basis Adjustment	(7)	(5)
Loans and leases | Hedged Items No Longer Designated
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount	112	11
Hedge Basis Adjustment	0	0
Long-term debt | Hedged Items Currently Designated
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount	15,960	16,163
Hedge Basis Adjustment	(117)	87
Long-term debt | Hedged Items No Longer Designated
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount	752	754
Hedge Basis Adjustment	$ 3	$ 4