Lease Obligations - Lessee - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lease Cost [Line Items]
Total finance lease costs	$ 5	$ 2	$ 9	$ 5
Total operating lease costs	35	31	96	92
Total lease costs	40	33	105	97
Impairment losses and termination charges	1	5	6	12
Net occupancy and equipment expense
Lease Cost [Line Items]
Amortization of ROU assets	4	2	7	5
Interest on long-term debt
Lease Cost [Line Items]
Interest on lease liabilities	1	0	2	0
Net occupancy expense
Lease Cost [Line Items]
Operating lease cost	29	25	76	72
Short-term lease cost	0	0	1	0
Variable lease cost	7	7	21	23
Sublease income	$ (1)	$ (1)	$ (2)	$ (3)