Commitments and Contingencies - Narrative - Environmental Matters (Details)						3 Months Ended	12 Months Ended	36 Months Ended	163 Months Ended
	Sep. 10, 2015	Sep. 20, 2011 unilateral_administrative_order	Mar. 14, 2008 a	May 09, 2002	Jun. 30, 2000 respondent water_company	Mar. 31, 2017 USD ($) LegalMatter	Dec. 31, 2002 USD ($) a	Dec. 31, 1997 respondent	Nov. 30, 2015 respondent	Dec. 31, 2016 USD ($)	Mar. 28, 2014	Mar. 27, 2014	Oct. 31, 2001 USD ($)
Site Contingency [Line Items]
Accrued environmental costs						$ 345,500,000				$ 349,700,000
Guarantee obligations						$ 120,000,000.0
Various Environmental Matters
Site Contingency [Line Items]
Number of environmental remediation matters (over) | LegalMatter						40
Environmental remediation term						15 years
Accrued environmental costs						$ 345,500,000
Various Environmental Matters | Minimum
Site Contingency [Line Items]
Estimated environmental costs						345,500,000
Various Environmental Matters | Maximum
Site Contingency [Line Items]
Estimated environmental costs						519,900,000
Various Environmental Matters | Sacramento, California
Site Contingency [Line Items]
Accrued environmental costs						207,800,000
Various Environmental Matters | Sacramento, California | Environmental Protection Agency
Site Contingency [Line Items]
Non-contaminated land | a							2,600
Number of Unilateral Administrative Orders | unilateral_administrative_order		2
Various Environmental Matters | Sacramento, California | Department of Toxic Substances Control
Site Contingency [Line Items]
Non-contaminated land | a			400
Various Environmental Matters | Sacramento, California | Minimum
Site Contingency [Line Items]
Estimated environmental costs						207,800,000
Various Environmental Matters | Sacramento, California | Maximum
Site Contingency [Line Items]
Estimated environmental costs						324,400,000
Guarantee obligations							$ 75,000,000
Various Environmental Matters | Sacramento, California | As Reported
Site Contingency [Line Items]
Guarantee obligations							$ 20,000,000
Various Environmental Matters | Baldwin Park Operable Unit
Site Contingency [Line Items]
Accrued environmental costs						$ 125,100,000
Guarantee obligations													$ 25,000,000
Number of other respondents | respondent									2
Number of water companies | water_company					5
Management agreement terms	10 years			15 years
Various Environmental Matters | Baldwin Park Operable Unit | Aerojet Rocketdyne, Inc.
Site Contingency [Line Items]
Percentage of responsibility in all project costs						74.00%					70.00%	68.00%
Various Environmental Matters | Baldwin Park Operable Unit | Environmental Protection Agency
Site Contingency [Line Items]
Number of other respondents | respondent					7			18
Various Environmental Matters | Baldwin Park Operable Unit | Minimum
Site Contingency [Line Items]
Estimated environmental costs						$ 125,100,000
Various Environmental Matters | Baldwin Park Operable Unit | Maximum
Site Contingency [Line Items]
Estimated environmental costs						175,300,000
Various Environmental Matters | Wabash, Indiana
Site Contingency [Line Items]
Accrued environmental costs						400,000
Expenditures recoverable						0
Various Environmental Matters | Wabash, Indiana | Minimum
Site Contingency [Line Items]
Estimated environmental costs						400,000
Various Environmental Matters | Wabash, Indiana | Maximum
Site Contingency [Line Items]
Estimated environmental costs						$ 700,000
Various Environmental Matters | Contracting Business
Site Contingency [Line Items]
Environmental obligation funding percent						99.00%