Guarantees, Commitments and Contingencies (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Guarantor Obligations [Line Items]
Guarantor Exposure as percent of outstanding loans	20.00%
Franchise lending program guarantee
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure	$ 43
Total loans outstanding	13
Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Exposure	$ 7
Property Lease Guarantee [Member]
Guarantor Obligations [Line Items]
Year longest lease expires	2065
Guarantor Obligations, Maximum Exposure	$ 550
Guarantee Obligations Maximum Exposure At Present Value	470
Franchise Loan Pool Guarantees [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Exposure	3
Total loans outstanding	$ 17