Derivative Financial Instruments (Hedges) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Yr	Dec. 31, 2013 Yr
Cash Flow Hedges [Member]
Net unrecognized after tax loss on active hedges recorded in AOCI	$ (181)	$ (127)
Net unrecognized after tax gain on terminated hedges recorded in AOCI to be recognized primarily 2016 to 2021	127	129
Estimated portion of net after-tax loss on active and terminated hedges to be reclassified from AOCI into earnings during the next 12 months	(51)	(50)
Maximum length of time entity has hedged portion of variable cash flows for forecasted transactions (in years)	8	7
Fair Value Hedges [Member]
Unrecognized pre-tax gain on terminated hedges to be recognized as interest through 2019	227	317
Portion of pre-tax gain on terminated hedges to be recognized as a change in interest expense during next 12 months	$ 88	$ 87