Earnings per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Earnings per Common Share [Abstract]
Net income	$ 33.8	$ 69.2	$ 159.3
Less: Net income attributable to noncontrolling interests	20.4	59.6	121.2
Net income attributable to Targa Resources Corp.	$ 13.4	$ 9.6	$ 38.1
Weighted average shares outstanding - basic (in shares)	41.6	41.0
Net income available per common share - basic (in dollars per share)	$ 0.32	$ 0.23	$ 0.93
Weighted average shares outstanding (in shares)	41.6	41.0
Dilutive effect of unvested stock awards (in shares)	0.4	0.8
Weighted average shares outstanding - diluted (in shares)	42.0	41.8
Net income available per common share - diluted (in dollars per share)	$ 0.32	$ 0.23	$ 0.91