Leases (Future Minimum Operating Lease Payments, Excluding Contingent Rentals) (Details) $ in Millions	Dec. 31, 2015 USD ($)
Operating Leased Assets [Line Items]
2016	$ 6
2017	8
2018	3
2019	2
2020	2
Thereafter	19
Total future minimum operating lease payments, excluding contingent rentals	40
IPL [Member]
Operating Leased Assets [Line Items]
2016	3
2017	3
2018	2
2019	1
2020	1
Thereafter	13
Total future minimum operating lease payments, excluding contingent rentals	23
WPL [Member]
Operating Leased Assets [Line Items]
2016	3
2017	5
2018	1
2019	0
2020	0
Thereafter	0
Total future minimum operating lease payments, excluding contingent rentals	$ 9