Derivatives and Hedging Activities - Credit Risk Contingent Feature (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	$ 2
One Rating Downgrade [Member] | Moody's, A3 Rating [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	$ 2
One Rating Downgrade [Member] | Standard & Poor's, A- Rating [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	2
Two Rating Downgrade [Member] | Moody's, A3 Rating [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	2
Two Rating Downgrade [Member] | Standard & Poor's, A- Rating [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	2
Three Rating Downgrade [Member] | Moody's, A3 Rating [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	2
Three Rating Downgrade [Member] | Standard & Poor's, A- Rating [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	$ 1	$ 2