Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2015 Subsequent Event [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Unrecognized Tax Benefits	$ 1,034		$ 1,069
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	922		939
Reported tax rate	8.90%	10.20%
Gross interest and penalties recognized in period	14
Net tax expense/benefits related to interest	9	9
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	416		402
Potential Reduction In Unrecognized Tax Benefits Over Next Twelve Months As Result Of Concluding Certain Matters				$ 15