Leases (Future Minimum Operating Lease Payments, Excluding Contingent Rentals) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Operating Leased Assets [Line Items]
2017	$ 6
2018	6
2019	2
2020	2
2021	1
Thereafter	15
Total future minimum operating lease payments, excluding contingent rentals	32
IPL [Member]
Operating Leased Assets [Line Items]
2017	3
2018	2
2019	1
2020	1
2021	1
Thereafter	10
Total future minimum operating lease payments, excluding contingent rentals	18
WPL [Member]
Operating Leased Assets [Line Items]
2017	3
2018	4
2019	0
2020	0
2021	0
Thereafter	0
Total future minimum operating lease payments, excluding contingent rentals	$ 7