Lease Obligations - Lessee - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Lease Cost [Line Items]
Total finance lease costs	$ 6	$ 5	$ 17	$ 9
Total operating lease costs	27	35	82	96
Total lease costs	33	40	99	105
Impairment losses and termination charges	1	1	3	6
Net occupancy and equipment expense
Lease Cost [Line Items]
Amortization of ROU assets	5	4	14	7
Interest on long-term debt
Lease Cost [Line Items]
Interest on lease liabilities	1	1	3	2
Net occupancy expense
Lease Cost [Line Items]
Operating lease cost	20	29	59	76
Short-term lease cost	0	0	1	1
Variable lease cost	8	7	24	21
Sublease income	$ (1)	$ (1)	$ (2)	$ (2)