Lease Obligations - Lessee - Lease Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Lessee Lease Description [Line Items]
Total right-of-use assets	$ 519	$ 507
Operating lease liabilities	553
Finance lease liabilities	46
Total lease liabilities	599	590
Finance lease right of use asset accumulated amortization	28	27
Operating lease right of use asset accumulated amortization	93	75
Other assets
Lessee Lease Description [Line Items]
Operating lease right-of-use assets	474	473
Bank premises and equipment
Lessee Lease Description [Line Items]
Finance lease right-of-use assets	45	34
Accrued taxes, interest and expenses
Lessee Lease Description [Line Items]
Operating lease liabilities	553	555
Long-term debt
Lessee Lease Description [Line Items]
Finance lease liabilities	$ 46	$ 35