Fair Value Measurements (Narrative) (Details) (USD $)	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	$ 10,200,000,000	$ 10,400,000,000
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	3,400,000,000	2,900,000,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Fair Value Disclosure	$ 10,700,000,000	$ 10,800,000,000