Commitments and Contingencies - Narrative - Environmental Matters (Details)					3 Months Ended	4 Months Ended	12 Months Ended		36 Months Ended	163 Months Ended
	Sep. 20, 2011 unilateral_administrative_order	Mar. 14, 2008 a	May. 09, 2002	Jun. 30, 2000 respondent water_company	Mar. 31, 2016 USD ($)	Mar. 31, 2016 USD ($) LegalMatter	Nov. 30, 2015 USD ($)	Dec. 31, 2002 USD ($) a	Dec. 31, 1997 respondent	Nov. 30, 2015 USD ($) respondent	Dec. 31, 2015 USD ($)	Mar. 28, 2014	Mar. 27, 2014	Oct. 31, 2001 USD ($)
Site Contingency [Line Items]
Accrued environmental costs					$ 299,300,000	$ 299,300,000	$ 306,100,000			$ 306,100,000	$ 302,300,000
Guarantee obligations					120,000,000.0	$ 120,000,000.0
Various Environmental Matters [Member]
Site Contingency [Line Items]
Number of environmental remediation matters | LegalMatter						40
Environmental remediation term						15 years	15 years
Accrued environmental costs					299,300,000	$ 299,300,000
Various Environmental Matters [Member] | Minimum [Member]
Site Contingency [Line Items]
Estimated environmental costs					299,300,000	299,300,000
Various Environmental Matters [Member] | Maximum [Member]
Site Contingency [Line Items]
Estimated environmental costs					452,700,000	452,700,000
Various Environmental Matters [Member] | Sacramento, California [Member]
Site Contingency [Line Items]
Accrued environmental costs					150,100,000	150,100,000
Guarantee obligations								$ 75,000,000
Various Environmental Matters [Member] | Sacramento, California [Member] | Minimum [Member]
Site Contingency [Line Items]
Estimated environmental costs					150,100,000	150,100,000
Various Environmental Matters [Member] | Sacramento, California [Member] | Maximum [Member]
Site Contingency [Line Items]
Estimated environmental costs					252,100,000	252,100,000
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					136,400,000	136,400,000
Guarantee obligations														$ 25,000,000
Number of other respondents | respondent										2
Number of water companies | water_company				5
Management agreement terms			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%			74.00%		70.00%	68.00%
Various Environmental Matters [Member] | Baldwin Park Operable Unit [Member] | Minimum [Member]
Site Contingency [Line Items]
Estimated environmental costs					136,400,000	136,400,000
Various Environmental Matters [Member] | Baldwin Park Operable Unit [Member] | Maximum [Member]
Site Contingency [Line Items]
Estimated environmental costs					179,900,000	179,900,000
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	200,000
Expenditures recoverable					0
Various Environmental Matters [Member] | Wabash, Indiana [Member] | Minimum [Member]
Site Contingency [Line Items]
Estimated environmental costs					200,000	200,000
Various Environmental Matters [Member] | Wabash, Indiana [Member] | Maximum [Member]
Site Contingency [Line Items]
Estimated environmental costs					$ 700,000	$ 700,000
Various Environmental Matters [Member] | Contracting business [Member]
Site Contingency [Line Items]
Environmental obligation funding percent					98.00%	98.00%