Summary of Significant Accounting Policies - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Income tax (benefit), net of refunds	$ 6,550	$ (102,154)	$ 18,537
Interest, net of amounts capitalized	170,209	177,074	184,010
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Accrued capital expenditures	83,798	44,712	33,184
Dividends declared but not paid	69,363	65,790	62,528
Liabilities assumed relating to acquisition of SCE Four Corners’ interest (see Note 3)	$ 0	$ 0	$ 145,609