Income Tax (Reconciliation of the Amount of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits, Increase Resulting from Acquisition	$ 0	$ 0	$ 1
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits Beginning balance, January 1	333	325	321
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions	281	264	256
Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions	(278)	(262)	(257)
Unrecognized Tax Benefits, Increases Resulting from Current Period Tax Positions	6	6	4
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	0	0	0
Unrecognized Tax Benefits Ending balance, December 31	$ 342	$ 333	$ 325