Investments (Summary Financial Information) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating revenues	$ 634	$ 611	$ 575
Operating income	334	326	307
Net income	248	234	218
Current assets	86	67
Non-current assets	3,553	3,321
Current liabilities	383	252
Non-current liabilities	1,682	1,652
WPL [Member]
Operating revenues	634	611	575
Operating income	334	325	308
Net income	250	239	226
Current assets	84	66
Non-current assets	3,527	3,292
Current liabilities	383	252
Non-current liabilities	$ 1,681	$ 1,651