Leases Leases - Maturity Table (Details) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year		$ 38
Lessee, Operating Lease, Liability, Payments, Due Year Two		139
Lessee, Operating Lease, Liability, Payments, Due Year Three		118
Lessee, Operating Lease, Liability, Payments, Due Year Four		96
Lessee, Operating Lease, Liability, Payments, Due Year Five		68
Lessee, Operating Lease, Liability, Payments, Due after Year Five		241
Lessee, Operating Lease, Liability, Payments, Due		700
Lessee, Operating Lease, Liability, Undiscounted Excess Amount		(126)
Operating Lease, Liability		574
Finance Lease, Liability, Payment, Due [Abstract]
Finance Lease, Liability, Payments, Remainder of Fiscal Year		16
Finance Lease, Liability, Payments, Due Year Two		70
Finance Lease, Liability, Payments, Due Year Three		76
Finance Lease, Liability, Payments, Due Year Four		69
Finance Lease, Liability, Payments, Due Year Five		58
Finance Lease, Liability, Payments, Due after Year Five		779
Finance Lease, Liability, Payment, Due		1,068
Finance Lease, Liability		517
Finance Lease, Liability, Undiscounted Excess Amount		(551)
Lease, Liability, Payments, Remainder of Fiscal Year		54	$ 216	[1]
Lease, Liability, Payments, Due Year Two		209	196	[1]
Lease, Liability, Payments, Due Year Three		194	183	[1]
Lease, Liability, Payments, Due Year Four		165	154	[1]
Lease, Liability, Payments, Due Year Five		126	117	[1]
Lease, Liability, Payments, Due after Year Five		1,020	931	[1]
Lease, Liability, Payments, Due		1,768	1,797	[1]
Lease, Liability, Undiscounted Excess Amount		(677)
Total Lease Liabilities		$ 1,091
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	[1]		147
Operating Leases, Future Minimum Payments, Due in Two Years	[1]		128
Operating Leases, Future Minimum Payments, Due in Three Years	[1]		110
Operating Leases, Future Minimum Payments, Due in Four Years	[1]		87
Operating Leases, Future Minimum Payments, Due in Five Years	[1]		61
Operating Leases, Future Minimum Payments, Due Thereafter	[1]		159
Operating Leases, Future Minimum Payments Due	[1]		692
Capital Leases, Future Minimum Payments, Net Present Value [Abstract]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	[1]		69
Capital Leases, Future Minimum Payments Due in Two Years	[1]		68
Capital Leases, Future Minimum Payments Due in Three Years	[1]		73
Capital Leases, Future Minimum Payments Due in Four Years	[1]		67
Capital Leases, Future Minimum Payments Due in Five Years	[1]		56
Capital Leases, Future Minimum Payments Due Thereafter	[1]		772
Capital Leases, Future Minimum Payments Due	[1]		$ 1,105

[1] (1) Amounts included for comparability and accounted for in accordance with ASC 840, "Leases".