Commitments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Estimated minimum lease payments for noncancelable operating leases
2012	$ 121
2013	102
2014	81
2015	43
2016	32
2017 and thereafter	85
Total	464
Barges and Rail Cars [Member]
Estimated minimum lease payments for noncancelable operating leases
2012	79
2013	68
2014	53
2015	21
2016	15
2017 and thereafter	10
Total	246
Other Capital Lease Payments [Member]
Estimated minimum lease payments for noncancelable operating leases
2012	42
2013	34
2014	28
2015	22
2016	17
2017 and thereafter	75
Total	218
Natural Gas [Member]
Total estimated minimum long-term obligations
2012	1,479
2013	1,553
2014	1,196
2015	998
2016	937
2017 and thereafter	2,798
Total	8,961
Coal [Member]
Total estimated minimum long-term obligations
2012	3,266
2013	2,218
2014	1,336
2015	592
2016	300
2017 and thereafter	737
Total	8,449
Nuclear Fuel [Member]
Total estimated minimum long-term obligations
2012	353
2013	197
2014	206
2015	145
2016	92
2017 and thereafter	740
Total	1,733
Purchased power [Member]
Total estimated minimum long-term obligations
2012	259
2013	248
2014	281
2015	311
2016	301
2017 and thereafter	2,700
Total	$ 4,100