Consolidated Income Statements - USD ($) shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Operating revenues	$ 7,648.5	$ 7,472.3	$ 5,926.1
Cost of sales	2,822.8	2,647.4	2,240.1
Other operation and maintenance	2,047.0	2,185.5	1,709.3
Depreciation and amortization	798.6	762.6	561.8
Property and revenue taxes	194.9	194.7	164.4
Total operating expenses	5,863.3	5,790.2	4,675.6
Operating Income	1,785.2	1,682.1	1,250.5
Equity in earnings of transmission affiliates	154.3	146.5	96.1
Other income, net	64.6	80.8	58.9
Interest expense	415.7	402.7	331.4
Other expense	(196.8)	(175.4)	(176.4)
Income before income taxes	1,588.4	1,506.7	1,074.1
Income tax expense	383.5	566.5	433.8
Net income	1,204.9	940.2	640.3
Preferred stock dividends of subsidiary	1.2	1.2	1.8
Net income attributed to common shareholders	$ 1,203.7	$ 939.0	$ 638.5
Earnings Per Share (Basic)
Earnings per common share (basic) (in dollars per share)	$ 3.81	$ 2.98	$ 2.36
Earnings Per Share (Diluted)
Earnings per common share (diluted) (in dollars per share)	$ 3.79	$ 2.96	$ 2.34
Weighted Average Common Shares Outstanding (Basic)
Basic (in shares)	315.6	315.6	271.1
Weighted Average Common Shares Outstanding (Diluted)
Diluted (in shares)	317.2	316.9	272.7

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

Name:	us-gaap_CostOfGoodsAndServicesSold
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Total costs of sales and operating expenses for the period.