Reportable Segments 2 Parentheticals (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Capital Expenditures [Abstract]
(Increase) Decrease Capital Accruals	$ 23.0	$ 9.5	$ 22.0

The increase or decrease in capital accrued for plant, property, and equipment.

No definition available.

Name:	sug_IncreaseDecreaseCapitalAccruals
Namespace Prefix:	sug_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration