Indebtedness (Senior Notes Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended	0 Months Ended	9 Months Ended
	Dec. 31, 2011	Dec. 31, 2011	Jun. 03, 2011 2.95% Senior Notes Maturing 2016 [Member]	Dec. 31, 2011 2.85% Senior Notes Maturing October 2013 [Member]	Dec. 31, 2011 4.5% Senior Notes Maturing September 2014 [Member]	Dec. 31, 2011 3.25% Senior Notes Maturing October 2015 [Member]	Dec. 31, 2011 Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 250	$ 300	$ 400	$ 250
Interest rate			2.95%	2.85%	4.50%	3.25%
Debt Instrument, Interest Rate, Effective Percentage			2.98%	2.871%	4.527%	3.283%
Interest payable terms			semi-annually on June 15 and December 15 of each year	semi-annually on April 1 and October 1 of each year	semi-annually on March 15 and September 15 of each year	semi-annually on April 1 and October 1 of each year
Maturity date			Jun. 15, 2016	Oct. 01, 2013	Sep. 15, 2014	Oct. 01, 2015
Percentage of principal that must be repaid in addition to accrued interest under call feature of notes	100.00%
Senior notes call feature description		103.563% of the principal amount					The 2013, 2014, 2015 and 2016 Notes (collectively, the “Senior Notes”) contain covenants that could restrict the incurrence of liens and limit sale and leaseback transactions. Additionally, the Company has the option to redeem the Senior Notes prior to their maturity, in whole or in part, at 100% of the principal plus any accrued but unpaid interest and applicable make-whole payments.