Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2016	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Unrecognized Tax Benefits	$ 1,056			$ 1,047
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	905			903
Reported tax rate	97.50%	8.90%
Gross interest and penalties recognized in period	16
Net tax expense/benefits related to interest and penalties	11	9
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	459			443
Subsequent Event [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Potential Reduction In Unrecognized Tax Benefits Over Next Twelve Months As Result Of Concluding Certain Matters			$ 10