Summary of Significant Accounting Policies Summary of Significant Accounting Policies - MEC - Income Taxes (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities, noncurrent		$ 7,309	$ 2,933
Regulatory assets		2,761	4,307
MidAmerican Energy Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities, noncurrent		1,661	883
Regulatory assets		204	1,161
Deferred Income Tax Charge [Member] | MidAmerican Energy Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Regulatory assets	[1]	0	985
Deferred Income Tax Charge [Member] | MidAmerican Energy Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Regulatory liabilities, noncurrent	[2]	$ 681	$ 0

[1] (1)Amounts primarily represent income tax benefits related to state accelerated tax depreciation and certain property-related basis differences that were previously passed on to customers and will be included in regulated rates when the temporary differences reverse.

[2] (3)Amount predominantly represents the excess of nuclear decommission trust assets over the related asset retirement obligation. Refer to Note 12 for a discussion of asset retirement obligations.