Leases (Summary of Financial Information Associated with Leases) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Assets
Operating lease right-of-use assets	$ 681	$ 688
Total leased assets	906	913
Current
Accrued expenses and other liabilities	178	178
Short-term debt and current maturities of long-term debt	$ 51	$ 60
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesAndOtherLiabilities	us-gaap:AccruedLiabilitiesAndOtherLiabilities
Long-term
Operating lease liabilities	$ 541	$ 549
Long-term debt	80	75
Total lease liabilities	850	862
Rental equipment
Assets
Finance lease, right-of-use asset, before accumulated amortization	296	295
Accumulated depreciation	(86)	(86)
Finance lease assets, net	210	209
Property and equipment, net
Assets
Accumulated depreciation	(13)	(11)
Finance lease assets, net	15	16
Non-rental vehicles
Assets
Finance lease, right-of-use asset, before accumulated amortization	8	8
Buildings
Assets
Finance lease, right-of-use asset, before accumulated amortization	$ 20	$ 19