Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash and securities collateral placed with counterparties	$ 12
Noncash collateral placed with counterparties	171	$ 118
Cash collateral received from counterparties	$ 2	40
Noncash collateral received from counterparties		$ 29