Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions						3 Months Ended	9 Months Ended
	Sep. 03, 2015	Jun. 05, 2015	Mar. 06, 2015	Jan. 13, 2015	Dec. 18, 2014	Sep. 30, 2015	Sep. 30, 2015	Jan. 12, 2015	Jan. 11, 2015
Class Of Stock [Line Items]
Common stock, shares authorized						450,000,000	450,000,000	450,000,000	3,000
Common stock, par or stated value per share						$ 0.01	$ 0.01	$ 0.01	$ 1
Cash dividends declared per share to shareholders						$ 0.225	$ 0.850
Cash Distribution Approved on September 3, 2015
Class Of Stock [Line Items]
Cash distribution declaration date							Sep. 03, 2015
Cash distributions to unit holders, date of record							Sep. 30, 2015
Dividends Payable, date declared							Sep. 03, 2015
Dividends payable date of record							Sep. 30, 2015
Cash dividends declared per share to shareholders	$ 0.225
Cash distribution and dividend payable date							Oct. 22, 2015
Cash Distribution Approved on June 5, 2015
Class Of Stock [Line Items]
Cash distribution declaration date							Jun. 05, 2015
Cash distributions to unit holders, date of record							Jun. 30, 2015
Dividends Payable, date declared							Jun. 05, 2015
Dividends payable date of record							Jun. 30, 2015
Cash dividends declared per share to shareholders		$ 0.225
Cash distribution and dividend paid date							Jul. 23, 2015
Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash distribution declaration date							Mar. 06, 2015
Cash distributions to unit holders, date of record							Mar. 31, 2015
Dividends Payable, date declared							Mar. 06, 2015
Dividends payable date of record							Mar. 31, 2015
Cash dividends declared per share to shareholders			$ 0.14
Cash distribution and dividend paid date							Apr. 23, 2015
Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash distribution declaration date							Jan. 13, 2015
Cash distributions to unit holders, date of record							Jan. 20, 2015
Dividends Payable, date declared							Jan. 13, 2015
Dividends payable date of record							Jan. 20, 2015
Cash dividends declared per share to shareholders				$ 0.26
Cash distribution and dividend paid date							Jan. 29, 2015
Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash distribution declaration date							Dec. 18, 2014
Cash distributions to unit holders, date of record							Dec. 18, 2014
Dividends Payable, date declared							Dec. 18, 2014
Dividends payable date of record							Dec. 18, 2014
Cash dividends declared per share to shareholders					$ 0.31
Cash distribution and dividend paid date							Jan. 16, 2015
Retained Earnings | Cash Distribution Approved on September 3, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders	$ 9.8
Retained Earnings | Cash Distribution Approved on June 5, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders		$ 9.8
Retained Earnings | Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders			$ 6.1
Retained Earnings | Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders				$ 9.0
Retained Earnings | Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash dividends declared to shareholders					$ 10.8
InfraREIT, L.L.C. | Cash Distribution Approved on September 3, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit	$ 0.225
Cash distribution to unit holders	$ 13.6
InfraREIT, L.L.C. | Cash Distribution Approved on June 5, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit		$ 0.225
Cash distribution to unit holders		$ 13.6
InfraREIT, L.L.C. | Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit			$ 0.14
Cash distribution to unit holders			$ 8.5
InfraREIT, L.L.C. | Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit				$ 0.26
Cash distribution to unit holders				$ 11.7
InfraREIT, L.L.C. | Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit					$ 0.31
Cash distribution to unit holders					$ 14.1
InfraREIT, L.L.C. | Retained Earnings | Cash Distribution Approved on September 3, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders	$ 9.8
InfraREIT, L.L.C. | Retained Earnings | Cash Distribution Approved on June 5, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders		$ 9.8
InfraREIT, L.L.C. | Retained Earnings | Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders			$ 6.1
InfraREIT, L.L.C. | Retained Earnings | Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders				$ 9.0
InfraREIT, L.L.C. | Retained Earnings | Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash dividends declared to shareholders					$ 10.8