Leases - Lease Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Operating Leases, under ASC 842
2020	$ 153
2021	139
2022	123
2023	104
2024	86
Thereafter	212
Total lease payments	817
Less: Interest	(74)
Present value of lease liabilities	743
Finance Leases, under ASC 842
2020	83
2021	73
2022	64
2023	10
2024	3
Thereafter	5
Total lease payments	238
Less: Interest	(16)
Present value of lease liabilities	222
Operating lease payments related to options to extend lease terms that are reasonably certain of being exercised	47
Minimum operating lease payments for leases signed but not yet commenced	4
Minimum finance lease payments for leases signed but not yet commenced	$ 302
Operating Leases, under ASC 840
2019		$ 94
2020		75
2021		62
2022		51
2023		40
Thereafter		108
Total		$ 430
Real Estate
Lessee, Lease, Description [Line Items]
Operating leases not yet commenced, term	5 years
Equipment
Lessee, Lease, Description [Line Items]
Finance leases not yet commenced, term	5 years

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Term of lessee's finance lease not yet commenced, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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