Lease Obligations - Lessee - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lease Cost [Line Items]
Total finance lease costs	$ 2	$ 1
Total operating lease costs	31	29
Total lease costs	33	30
Net occupancy and equipment expense
Lease Cost [Line Items]
Amortization of right-of-use assets	1	1
Interest Expense, Long-Term Debt
Lease Cost [Line Items]
Interest on lease liabilities	1
Net occupancy expense
Lease Cost [Line Items]
Operating lease cost	24	22
Short-term lease cost	1
Variable lease cost	7	8
Sublease income	$ (1)	$ (1)