Contingencies (Federal Government's Lawsuit) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended								72 Months Ended
	Aug. 31, 2006	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, 2019
Loss Contingencies [Line Items]
Provision related to litigation recorded		$ 7	$ 34	$ 18	$ 24	$ 29	$ 3	$ 28	$ 17
Federal Governments Lawsuit [Member]
Loss Contingencies [Line Items]
Disclosure period	10 years
Implementation of Corrective Communications [Member] | Federal Governments Lawsuit [Member]
Loss Contingencies [Line Items]
Provision related to litigation recorded										$ 36