Summary of Significant Accounting Policies - MidAmerican Funding - Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
MidAmerican Funding, LLC and Subsidiaries [Domain]
Goodwill [Line Items]
Goodwill impairment	$ 0	$ 0	$ 0

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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