Segment and Revenue Information (Revenue by Type) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 6,874	$ 5,837	$ 6,075	$ 6,499	$ 6,656	$ 6,481	$ 6,925	$ 6,936	$ 25,285	$ 26,998	$ 26,425
United States [Member]
Disaggregation of Revenue [Line Items]
Revenues									20,690	21,449	20,442
Non-US [Member]
Disaggregation of Revenue [Line Items]
Revenues									$ 4,595	$ 5,549	$ 5,983