INVESTMENT IN ATC - INCOME STATEMENT AND BALANCE SHEET (Details) (ATC, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
ATC
Income statement data
Revenues	$ 163.3	$ 151.8
Operating expenses	78.6	69.8
Other expense	21.6	21.5
Net income	63.1	60.5
Balance sheet data
Current assets	79.2		80.7
Noncurrent assets	3,563.9		3,509.5
Total assets	3,643.1		3,590.2
Current liabilities	301.4		381.5
Long-term debt	1,650.0		1,550.0
Other noncurrent liabilities	131.2		126.1
Shareholders' equity	1,560.5		1,532.6
Total liabilities and shareholders' equity	$ 3,643.1		$ 3,590.2