Acquisition of Oiltanking Partners, L.P., Pro Forma Earnings Data (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Basic earnings per unit [Abstract]
As reported basic units outstanding (in units)									1,848.7	1,788.0	1,723.6
As reported basic earnings per unit (in dollars per unit)	$ 0.35	$ 0.38	$ 0.35	$ 0.44	$ 0.38	$ 0.33	$ 0.31	$ 0.43	$ 1.51	$ 1.45	$ 1.40
Diluted earnings per unit [Abstract]
As reported diluted units outstanding (in units)									1,895.2	1,842.6	1,786.4
As reported diluted earnings per unit (in dollars per unit)	$ 0.34	$ 0.37	$ 0.34	$ 0.43	$ 0.37	$ 0.32	$ 0.30	$ 0.41	$ 1.47	$ 1.41	$ 1.35
Oiltanking Partners L.P. [Member]
Pro forma earnings data [Abstract]
Revenues									$ 48,087.5	$ 47,875.7
Costs and expenses									44,509.0	44,522.3
Operating income									3,838.0	3,520.7
Net income									2,877.5	2,632.8
Net income attributable to noncontrolling interest									75.0	39.5
Net income attributable to limited partners									$ 2,802.5	$ 2,593.3
Basic earnings per unit [Abstract]
As reported basic units outstanding (in units)									1,848.7	1,788.0
Pro forma basic units outstanding (in units)									1,903.5	1,842.8
As reported basic earnings per unit (in dollars per unit)									$ 1.51	$ 1.45
Pro forma basic earnings per unit (in dollars per unit)									$ 1.47	$ 1.41
Diluted earnings per unit [Abstract]
As reported diluted units outstanding (in units)									1,895.2	1,842.6
Pro forma diluted units outstanding (in units)									1,950.0	1,897.4
As reported diluted earnings per unit (in dollars per unit)									$ 1.47	$ 1.41
Pro forma diluted earnings per unit (in dollars per unit)									$ 1.44	$ 1.37