Income Taxes (Reconciliation of Income Tax Expense to the Statutory Federal Income Tax Rate) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	$ 922	$ 960	$ 991
Income tax expense at 35% statutory rate	323	336	347
Production tax credits	(68)	(49)	(6)
Investment tax credits	(6)	(6)	(6)
Depreciation	(4)	(4)	(4)
AFUDC - Equity	(5)	(4)	(1)
Employee Stock Ownership Plan dividends	(4)	(4)	(4)
Domestic production activities deduction	(14)	(14)	(7)
State and Local income taxes, net of federal benefit	37	37	37
Enactment of Michigan Corporate income Tax, net of federal expense	0	0	(87)
Other, net	(5)	(6)	(1)
Income Tax Expense (Benefit)	$ 254	$ 286	$ 268
Effective Income Tax Rate	27.50%	29.80%	27.00%