Derivatives and Hedging Activities - Credit Risk Contingent Feature (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	$ 4
Standard & Poor's, A- Rating [Member] | One Rating Downgrade [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	$ 1
Standard & Poor's, A- Rating [Member] | Two Rating Downgrade [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	1
Standard & Poor's, A- Rating [Member] | Three Rating Downgrade [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	1
Moody's, A3 Rating [Member] | One Rating Downgrade [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	1
Moody's, A3 Rating [Member] | Two Rating Downgrade [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	1	1
Moody's, A3 Rating [Member] | Three Rating Downgrade [Member]
Credit Derivatives [Line Items]
Additional collateral aggregate fair value	$ 1	$ 1