Description of Business and Significant Accounting Policies Settlement Assets and Settlement Liabilities (Details) - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
---|---|---|
Revenue from Contract with Customer [Abstract] | ||
Settlement Assets, Current | $ 33 | $ 33 |
Settlement Liabilities, Current | $ 31 | $ 31 |