Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Noncash collateral placed with counterparties	$ 119	$ 105
Cash collateral placed with counterparties		26
Cash collateral received from counterparties	53	30
Noncash collateral received from counterparties	$ 38	$ 3