Derivative Instruments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Credit Derivatives [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ 39,000,000
Cash flow hedge, reclassified to earnings, net	0	$ 0
Non-performance Risk Adjustment	0
Exposure Associated With Collateralization Events	0		$ 0
Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Exposure	$ 0		$ 0