Summary of Significant Accounting Policies (Net Interest) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Accounting Policies [Abstract]
Interest expense	$ 489	$ 472		$ 374
Interest income	(12)	(12)		(18)
Interest expense, net	$ 477	$ 460	[1]	$ 356	[1]

[1] *Prior-period information has been restated for the retrospective application of a change in accounting principle related to the amortization of actuarial gains and losses for our qualified U.S. government pension plans, which we adopted in the fourth quarter of 2020. For further discussion of this change in accounting principle, see Note T to the Consolidated Financial Statements.