Subsequent Events (Details) (USD $)	Jul. 27, 2011	Jun. 30, 2011
Subsequent Event [Line Items]
Unsecured revolving credit facility		$ 1,150,000,000
Applicable margin Over LIBOR, based on certain debt ratings	1.35%	0.60%
Annual facility fee for each bank based on commitment amount	0.25%	0.15%
Original [Member]
Subsequent Event [Line Items]
Unsecured revolving credit facility	1,150,000,000
Replacement [Member]
Subsequent Event [Line Items]
Unsecured revolving credit facility	2,000,000,000

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 129
-Paragraph 2, 4

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 22
-Article 5

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant