Derivatives and Risk Management (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) item
Derivative [Line Items]
Number of derivative positions designated for hedge accounting | item	0
Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative assets	$ 1
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative assets	77
Not Designated as Hedging Instrument [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Notional amount	$ 170
Derivative, expiration	Jun. 30, 2020
Derivative assets	$ 1