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Basis Of Presentation Derivative Instruments (Details) - Interest Rate Swap - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Derivative [Line Items]
Derivative, Notional Amount	$ 1,000
Not Designated as Hedging Instrument \| Interest expense
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(13)	$ 51
Not Designated as Hedging Instrument \| Other non-current liabilities
Derivative [Line Items]
Interest rate swap contract - other current and non-current liabilities	63		$ 81
November 2017
Derivative [Line Items]
Derivative, Notional Amount	450
August 2020
Derivative [Line Items]
Derivative, Notional Amount	400
November 2022
Derivative [Line Items]
Derivative, Notional Amount	$ 150