Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Advertising Expense) (Details)

v3.20.4
Summary of Significant Accounting Policies (Advertising Expense) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Accounting Changes and Error Corrections [Abstract]      
Advertising Expense $ 57 $ 115 $ 92