Income Tax Provision (Components of Income Tax Expense and Effective Income Tax Rate Reconciliation ) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Deferred
Total Deferred			$ 588	$ 334
Provision for income taxes	$ 185	$ 113	$ 574	$ 315
Reconciliation Between U.S. Federal Statutory Tax Rate and Effective Tax Rate
Effective tax rate	38.00%	37.00%	37.00%	37.00%