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Contingencies (Federal Government's Lawsuit) (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended 12 Months Ended
Aug. 31, 2006
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2014
Loss Contingencies [Line Items]                    
Provision related to litigation recorded   $ 29 $ 3 $ 28 $ 17 $ 12 $ 21 $ 70 $ 28  
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   $ 5               $ 31