Revenue Recognition Contract Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Contract With Customer, Liability [Line Items]
Contract with Customer, Liability - Beginning of Period	$ 1,171	$ 1,189	$ 1,209	$ 1,215
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	72	74	85	102
Other Significant Noncash Transaction, Value of Consideration Received	2	2	5	5
Contract with Customer, Liability, Revenue Recognized	(52)	(62)	(106)	(119)
Contract with Customer, Liability - End of Period	$ 1,193	$ 1,203	$ 1,193	$ 1,203