Contingencies (Details) $ in Millions	3 Months Ended
	Jun. 30, 2018 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	$ 27
Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Exposure	$ 11
Property Lease Guarantee [Member]
Guarantor Obligations [Line Items]
Year longest lease expires	2065
Guarantor Obligations, Maximum Exposure	$ 600
Guarantee Obligations Maximum Exposure At Present Value	500
Franchise Loan Pool Guarantees [Member] | Guarantee of Indebtedness of Others [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Exposure	2
Total loans outstanding	$ 11