Leases (Summary of Supplemental Balance Sheet Information Related to Operating Leases) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets:
Operating lease assets	$ 387	$ 346
Liabilities:
Current lease liabilities	42	61
Non-current lease liabilities	397	331
Total lease liabilities	$ 439	$ 392
Current lease liability, statement of financial position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent