Description of Business and Basis of Presentation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		9 Months Ended			0 Months Ended		0 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended		6 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended	0 Months Ended					0 Months Ended			6 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended	0 Months Ended				0 Months Ended		6 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended
	Apr. 02, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Aug. 02, 2013	Apr. 02, 2013 Over-Allotment Option	Oct. 24, 2014 Subsequent Event Support Agreement	Jul. 16, 2014 Minimum	Sep. 30, 2014 Minimum	Sep. 30, 2014 Minimum Gathering Systems	Jul. 16, 2014 Maximum	Sep. 30, 2014 Maximum	Sep. 30, 2014 Maximum Gathering Systems	Jun. 30, 2014 GIP I Entities and GIP II	Sep. 30, 2014 Williams Acquisition	Jun. 30, 2014 Williams Acquisition	Sep. 30, 2014 Williams Acquisition	Oct. 26, 2014 Merger Agreement Subsequent Event	Oct. 26, 2014 Merger Agreement Public Exchange Ratio Subsequent Event	Oct. 26, 2014 Merger Agreement Williams Parties Exchange Ratio Subsequent Event	Mar. 31, 2014 MidCon Compression, L.L.C. hp	Mar. 31, 2014 MidCon Compression, L.L.C. Minimum Compression	Apr. 02, 2013 Common Units	Oct. 24, 2014 Common Units Subsequent Event Support Agreement	Jun. 30, 2014 Common Units GIP I Entities and GIP II	Jun. 30, 2014 Common Units Williams Acquisition	Sep. 30, 2014 Common Units Williams Acquisition	Jun. 30, 2014 Common Units Publicly Owned	Sep. 30, 2014 Common Units Publicly Owned	Oct. 26, 2014 Common Units Merger Agreement Subsequent Event	Jun. 30, 2014 Class B Units GIP I Entities and GIP II	Sep. 30, 2014 Class B Units Williams Acquisition	Jun. 30, 2014 Class B Units Williams Acquisition	Oct. 26, 2014 Class B Units Merger Agreement Subsequent Event	Oct. 24, 2014 Class D Units Subsequent Event Support Agreement	Jun. 30, 2014 General Partner	Sep. 30, 2014 General Partner	Jun. 30, 2014 General Partner GIP I Entities and GIP II	Sep. 30, 2014 General Partner Williams Acquisition
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Units outstanding															2,068,692											48,742,361	40,137,695	88,880,056	101,171,762	101,915,143		6,340,022	12,800,906	6,340,022			2,068,692			4,155,023
General partnership interest	2.00%			2.00%											50.00%				2.00%								50.00%	100.00%									1.00%	2.00%	1.00%	100.00%
Limited partnership interest															26.60%		22.50%	48.90%											48.90%	49.10%
Award vesting period									1 year	4 years		4 years	5 years
Stock-based compensation expense		$ 83.6	$ 5.8	$ 107.4	$ 22.2											$ 96.0
Common Unit Exchange Ratio																				0.86672	0.80036
General partnership interest																			one-for-one
Pre-Merger Unit Split																															1.06152				1.06152
Shares, Outstanding																									279,472,244											26,475,507
Ownership interest								65.63%
Consideration paid for acquisition																						160
Number of compression units acquired																							100
Combined capacity of compression units																						200,000
Market value of common units						300.0
Common stock, shares issued		0		909,219			1,350,000																	10,350,000
Net offering proceeds	399.8			52.2
Payments for commissions				0.5
Capital contribution from Partnerships' general partner	8.4	1.0		1.0
Common stock, par value	$ 39.86
Gathering systems useful lives											20 years			30 years
Changes in estimated result of depreciation expense		29.7		29.7
Changes in estimated result of depreciation expense, per unit		$ 0.16		$ 0.16
Changes in estimated result of unconsolidated affiliates		4.6		4.6
Changes in estimated result of unconsolidated affiliates, per unit		$ 0.02		$ 0.02
Changes in estimated result of net income		$ 34.3		$ 34.3
Changes in estimated result of net income, per unit		$ 0.18		$ 0.18