Investments (Summary Financial Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues	$ 724	$ 741	$ 658
Operating income	325	374	331
Net income	217	267	232
Current assets	144	104
Non-current assets	5,498	5,041
Current liabilities	644	770
Non-current liabilities	2,315	2,038
Noncontrolling interest	223	255
WPL [Member]
Revenues	8	8	658
Operating income	2	4	331
Net income	1	2	$ 234
Current assets	4	7
Non-current assets	19	20
Current liabilities	1	2
Non-current liabilities	6	8
Noncontrolling interest	$ 0	$ 0