Lease Obligations - Lessee - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lease Cost [Line Items]
Total finance lease costs	$ 5	$ 2	$ 11	$ 4
Total operating lease costs	27	29	55	60
Total lease costs	32	31	66	64
Impairment losses and termination charges	2	3	2	5
Net occupancy and equipment expense
Lease Cost [Line Items]
Amortization of ROU assets	4	2	9	3
Interest on long-term debt
Lease Cost [Line Items]
Interest on lease liabilities	1	0	2	1
Net occupancy expense
Lease Cost [Line Items]
Operating lease cost	19	22	39	46
Short-term lease cost	0	0	1	1
Variable lease cost	8	7	16	14
Sublease income	$ 0	$ 0	$ (1)	$ (1)