Derivatives and Hedging Activities - Credit Risk Contingent Feature (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	$ 2
Standard & Poor's, A- Rating | One rating downgrade
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	$ 1
Standard & Poor's, A- Rating | Two rating downgrades
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	2	1
Standard & Poor's, A- Rating | Three rating downgrades
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	2	1
Moody's, A3 Rating | One rating downgrade
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	1
Moody's, A3 Rating | Two rating downgrades
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	2	1
Moody's, A3 Rating | Three rating downgrades
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	$ 2	$ 1