Commitments and Contingencies - Narrative - Environmental Matters (Details)		3 Months Ended	12 Months Ended
	May 09, 2017	Mar. 31, 2020 USD ($) legal_matter	Dec. 31, 2002 USD ($) a respondent water_company	Dec. 31, 2019 USD ($)	Oct. 31, 2001 USD ($)
Site Contingency [Line Items]
Accrued environmental costs		$ 302,600,000		$ 309,200,000
Guarantee obligations		$ 120,000,000.0
Various Environmental Matters
Site Contingency [Line Items]
Number of environmental remediation matters (over) | legal_matter		40
Accrued environmental costs		$ 302,600,000
Environmental obligation funding percent		99.00%
Various Environmental Matters | Sacramento, California
Site Contingency [Line Items]
Accrued environmental costs		$ 204,200,000
Various Environmental Matters | Sacramento, California | Environmental Protection Agency
Site Contingency [Line Items]
Non-contaminated land | a			2,600
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		$ 84,800,000
Guarantee obligations					$ 25,000,000
Various Environmental Matters | Baldwin Park Operable Unit | Aerojet Rocketdyne, Inc.
Site Contingency [Line Items]
Percentage of responsibility in all project costs		74.00%
Various Environmental Matters | Baldwin Park Operable Unit | Environmental Protection Agency
Site Contingency [Line Items]
Number of respondents | respondent			7
Number of water companies | water_company			5
Term of arrangement (years)	10 years
Various Environmental Matters | Minimum
Site Contingency [Line Items]
Estimated environmental costs		$ 302,600,000
Various Environmental Matters | Minimum | Sacramento, California
Site Contingency [Line Items]
Estimated environmental costs		204,200,000
Various Environmental Matters | Minimum | Baldwin Park Operable Unit
Site Contingency [Line Items]
Estimated environmental costs		84,800,000
Various Environmental Matters | Maximum
Site Contingency [Line Items]
Estimated environmental costs		453,700,000
Various Environmental Matters | Maximum | Sacramento, California
Site Contingency [Line Items]
Estimated environmental costs		327,400,000
Guarantee obligations			$ 75,000,000
Various Environmental Matters | Maximum | Baldwin Park Operable Unit
Site Contingency [Line Items]
Estimated environmental costs		$ 100,900,000