Equity Total Comprehensive Income, Equity and their Components (Parenthetical) (Details) (USD $)	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Stockholders Equity Note [Line Items]
Dividends on common stock	$ 0.6600	$ 0.6275
Dividends on noncontrolling interest units	$ 0.6600	$ 0.6275

Aggregate dividends declared during the period for each share of common stock outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration