Derivative Instruments and Hedging Activities Gain/Loss in Income (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Other Assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 158	$ 75
Other Assets [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	158	75
Other Assets [Member] | Not Designated As Hedging Instruments [Member] | Offsetting Interest Rate Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	5	33
Other Assets [Member] | Not Designated As Hedging Instruments [Member] | Interest Rate Swaps For Customers [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	146	37
Other Assets [Member] | Not Designated As Hedging Instruments [Member] | Fair Value Hedging [Member] | Offsetting Interest Rate Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	5	33
Other Assets [Member] | Not Designated As Hedging Instruments [Member] | Fair Value Hedging [Member] | Interest Rate Swaps For Customers [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	141	7
Other Liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liability, Fair Value, Gross Liability	167	76
Other Liabilities [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liability, Fair Value, Gross Liability	167	76
Other Liabilities [Member] | Not Designated As Hedging Instruments [Member] | Offsetting Interest Rate Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liability, Fair Value, Gross Liability	157	40
Other Liabilities [Member] | Not Designated As Hedging Instruments [Member] | Interest Rate Swaps For Customers [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liability, Fair Value, Gross Liability	5	33
Other Liabilities [Member] | Not Designated As Hedging Instruments [Member] | Fair Value Hedging [Member] | Offsetting Interest Rate Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liability, Fair Value, Gross Liability	9	3
Other Liabilities [Member] | Not Designated As Hedging Instruments [Member] | Fair Value Hedging [Member] | Interest Rate Swaps For Customers [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 5	$ 33