Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Segment Total Assets [Line Items]
Total assets	$ 32,286,082	$ 31,633,973
US Segment Reporting Information [Member]
Segment Total Assets [Line Items]
Total assets	19,041,229	17,965,559
Canada Segment Reporting Information [Member]
Segment Total Assets [Line Items]
Total assets	3,560,286	3,347,771
Europe And South Africa Segment Reporting Information [Member]
Segment Total Assets [Line Items]
Total assets	1,851,560	1,846,751
Asia Pacific Segment Reporting Information [Member]
Segment Total Assets [Line Items]
Total assets	2,879,894	2,902,101
Corporate And Other Segment Reporting Information [Member]
Segment Total Assets [Line Items]
Total assets	$ 4,953,113	$ 5,571,791