Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Schedule of Property, Plant and Equipment

Property, plant and equipment consisted of the following assets:

(millions)	Estimated Useful Lives	December 31, 2018			December 31, 2017
Electric generation	21-56 years	$	5,038		$	4,766
Electric transmission	28-77 years		880			859
Electric distribution	14-56 years		2,568			2,437
Gas transmission and distribution	16-77 years		1,678			1,534
General plant and other	8-43 years		613			579
Total cost			10,777			10,175
Less accumulated depreciation			(3,214	)		(2,994	)
Construction work in progress			673			263
Total property, plant and equipment, net		$	8,236		$	7,444