Derivatives (Details 2-Fair Value Hedges) - Fair Value Hedging [Member] - Designated as Hedging Instrument [Member] - Interest Rate Contract [Member] - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Debentures Due 2017 [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 600	$ 600
Weighted-average, LIBOR-based, floating rate	4.92%	4.73%
Debentures Due 2018 [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 300	$ 300
Weighted-average, LIBOR-based, floating rate	4.77%	4.66%