Leases - Summary (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating Lease, Right-of-Use Asset	$ 517	$ 525
Finance Lease, Right-of-Use Asset	501	504
Total Right-of-Use Asset	1,018	1,029
Operating Lease, Liability	569
Finance Lease, Liability	514
Total Lease Liabilities	1,083	1,096
Lessee, Lease, Description [Line Items]
Operating Lease, Liability	569
Finance Lease, Liability	514
Other Liabilities
Leases [Abstract]
Operating Lease, Liability	569	577
Lessee, Lease, Description [Line Items]
Operating Lease, Liability	569	577
Other Noncurrent Liabilities [Member]
Leases [Abstract]
Finance Lease, Liability	514	519
Lessee, Lease, Description [Line Items]
Finance Lease, Liability	$ 514	$ 519