Commitments and Contingencies - Environmental Matters (Details)							12 Months Ended		36 Months Ended	163 Months Ended
	Sep. 10, 2015	Feb. 28, 2015 a	Sep. 20, 2011 unilateral_administrative_order	Mar. 14, 2008 a	May 09, 2002	Jun. 30, 2000 respondent water_company	Dec. 31, 2016 USD ($) LegalMatter	Dec. 31, 2002 USD ($) a	Dec. 31, 1997 respondent	Nov. 30, 2015 USD ($) respondent	Sep. 30, 2016	Dec. 31, 2015 USD ($)	Nov. 30, 2014 USD ($)	Mar. 28, 2014	Mar. 27, 2014	Nov. 30, 2013 USD ($)	Oct. 31, 2001 USD ($)
Site Contingency [Line Items]
Accrued environmental costs							$ 349,700,000			$ 306,100,000		$ 302,300,000	$ 166,000,000			$ 171,300,000
Guarantee obligations							$ 120,000,000.0
Non-contaminated land | a		5,563
Various Environmental Matters [Member]
Site Contingency [Line Items]
Number of environmental remediation matters (over) | LegalMatter							40
Accrued environmental costs							$ 349,700,000
Various Environmental Matters [Member] | Sacramento, California [Member]
Site Contingency [Line Items]
Accrued environmental costs							210,100,000
Various Environmental Matters [Member] | Sacramento, California [Member] | Environmental Protection Agency [Member]
Site Contingency [Line Items]
Non-contaminated land | a								2,600
Number of Unilateral Administrative Orders | unilateral_administrative_order			2
Various Environmental Matters [Member] | Sacramento, California [Member] | Department of Toxic Substances Control [Member]
Site Contingency [Line Items]
Non-contaminated land | a				400
Various Environmental Matters [Member] | Sacramento, California [Member] | Previously Reported [Member]
Site Contingency [Line Items]
Guarantee obligations								$ 20,000,000
Various Environmental Matters [Member] | Baldwin Park Operable Unit [Member]
Site Contingency [Line Items]
Accrued environmental costs							126,800,000
Guarantee obligations																	$ 25,000,000
Number of other respondents | respondent										2
Number of water companies | water_company						5
Management agreement terms	5 years				15 years
Various Environmental Matters [Member] | Baldwin Park Operable Unit [Member] | Aerojet Rocketdyne, Inc. [Member]
Site Contingency [Line Items]
Percentage of responsibility in all project costs											74.00%			70.00%	68.00%
Various Environmental Matters [Member] | Baldwin Park Operable Unit [Member] | Environmental Protection Agency [Member]
Site Contingency [Line Items]
Number of other respondents | respondent						7			18
Various Environmental Matters [Member] | Wabash, Indiana [Member]
Site Contingency [Line Items]
Accrued environmental costs							200,000
Expenditures recoverable							$ 0
Various Environmental Matters [Member] | Contracting business [Member]
Site Contingency [Line Items]
Environmental obligation funding percent							99.00%
Various Environmental Matters [Member] | Minimum [Member]
Site Contingency [Line Items]
Estimated environmental costs							$ 349,700,000
Various Environmental Matters [Member] | Minimum [Member] | Sacramento, California [Member]
Site Contingency [Line Items]
Estimated environmental costs							210,100,000
Various Environmental Matters [Member] | Minimum [Member] | Baldwin Park Operable Unit [Member]
Site Contingency [Line Items]
Estimated environmental costs							126,800,000
Various Environmental Matters [Member] | Minimum [Member] | Wabash, Indiana [Member]
Site Contingency [Line Items]
Estimated environmental costs							200,000
Various Environmental Matters [Member] | Maximum [Member]
Site Contingency [Line Items]
Estimated environmental costs							525,000,000
Various Environmental Matters [Member] | Maximum [Member] | Sacramento, California [Member]
Site Contingency [Line Items]
Estimated environmental costs							326,000,000
Guarantee obligations								$ 75,000,000
Various Environmental Matters [Member] | Maximum [Member] | Baldwin Park Operable Unit [Member]
Site Contingency [Line Items]
Estimated environmental costs							178,300,000
Various Environmental Matters [Member] | Maximum [Member] | Wabash, Indiana [Member]
Site Contingency [Line Items]
Estimated environmental costs							$ 700,000