(Commercial Paper Program) (Details) (USD $) In Billions, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Line of Credit Facility [Line Items]
Size of total commercial paper program	$ 1.2
Commitment fee	15 to 35 basis points, depending on credit rating and currently pay a commitment fee of 20 basis points
Commitment fee, minimum percentage to pay depending on credit rating	0.15%
Commitment fee, maximum percentage to pay depending on credit rating	0.35%
Commitment fee, current percentage	0.20%
Indebtedness to cash flow	4
3 Year Facility [Member]
Line of Credit Facility [Line Items]
Size of total commercial paper program	$ 1.2

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

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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