Lease Obligations - Lessee - Lease Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Lease Cost [Line Items]
Total finance lease costs	$ 7
Total operating lease costs	124
Total lease costs	131
Net occupancy and equipment expense
Lease Cost [Line Items]
Amortization of right-of-use assets	6
Interest Expense, Long-Term Debt
Lease Cost [Line Items]
Interest on lease liabilities	1
Net occupancy expense
Lease Cost [Line Items]
Operating lease cost	96
Short-term lease cost	1
Variable lease cost	30
Sublease income	$ (3)