Derivatives (Details 2-Fair Value Hedges) (Designated as Hedging Instrument [Member]) In Millions, unless otherwise specified	Dec. 31, 2014 Interest Rate Contract [Member] Debentures Due 2017 [Member]	Dec. 31, 2013 Interest Rate Contract [Member] Debentures Due 2017 [Member]	Dec. 31, 2014 Interest Rate Contract [Member] Debentures Due 2017 [Member] Fair Value Hedging [Member] USD ($)	Dec. 31, 2013 Interest Rate Contract [Member] Debentures Due 2017 [Member] Fair Value Hedging [Member] USD ($)	Dec. 31, 2014 Interest Rate Contract [Member] Notes Due 2018 [Member]	Dec. 31, 2013 Interest Rate Contract [Member] Notes Due 2018 [Member]	Dec. 31, 2014 Interest Rate Contract [Member] Notes Due 2018 [Member] Fair Value Hedging [Member] USD ($)	Dec. 31, 2013 Interest Rate Contract [Member] Notes Due 2018 [Member] Fair Value Hedging [Member] USD ($)	Dec. 31, 2013 Foreign Exchange Contract [Member] Fair Value Hedging [Member] NOK
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount			$ 600	$ 600			$ 300	$ 300	2,387
Derivative, Average Forward Exchange Rate									6.060
Weighted-average, LIBOR-based, floating rate	4.64%	4.65%			4.49%	4.50%