Supplemental Financial Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash paid for interest	$ 965	$ 922	$ 1,012
Cash paid (refunded) for income taxes	466	598	157
Continuing Operations [Member]
Cash and Cash Equivalents [Line Items]
Cash paid (refunded) for income taxes	411	560	153
Discontinued Operations [Member]
Cash and Cash Equivalents [Line Items]
Cash paid (refunded) for income taxes	$ 55	$ 38	$ 4