Debt and Financing Activities Debt and Financing Activities (Long-Term Debt) (Narrative) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended		1 Months Ended		1 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Days	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 0.95% Notes Due December 4, 2015 [Member]	Dec. 04, 2012 0.95% Notes Due December 4, 2015 [Member]	Dec. 31, 2012 2.70% Notes Due December 15, 2022 [Member]	Dec. 04, 2012 2.70% Notes Due December 15, 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						0.95%		2.70%
Debt Instrument, Maturity Date					Dec. 04, 2015		Dec. 15, 2022
Debt Instrument, Face Amount						$ 500		$ 400
Debt Instrument, Date of First Required Payment					Jun. 04, 2013		Jun. 15, 2013
Proceeds from Issuance of Long-term Debt	$ 892		$ 892	$ 0
Number Of Days Notice Before Notes Can Be Redeemed		30
Contingent purchase offer, Series		101.00%