Statement of Cash Flows, Supplemental Information (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Cash payments related to operating lease liabilities	[1]	$ 538	$ 541	$ 0
Interest paid		653	661
Interest paid				619
Income taxes paid (refund)		19	16	17
New ROU assets obtained in exchange for operating lease liabilities		627	431	0
Increase (Decrease) in accounts payable for purchases of property and equipment		27	2	29
Purchase of property and equipment under capital leases and installment purchases		33	33	40
Cash and cash equivalents		232	196	277
Restricted cash		144	137	131
Restricted Cash, Noncurrent		5	5	5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents		$ 381	$ 338	$ 413

[1] Excludes the Company's contingent payments pursuant to operating leases, which are recorded as expense in the period such contingencies are resolved.