Stockholders' Equity - Changes in Stockholders' Equity (Details) (USD $)	3 Months Ended				6 Months Ended			12 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013	Jun. 30, 2012		Dec. 31, 2012
Changes in Stockholders' Equity
Beginning Balance					$ 19,004,000,000	$ 18,285,000,000		$ 18,285,000,000
Net Income After Dividends on Preferred and Preference Stock	297,000,000	[1],[2]	623,000,000	[1]	378,000,000	991,000,000	[1]
Other comprehensive income (loss)	5,000,000		(7,000,000)		9,000,000	(1,000,000)
Stock issued					293,000,000	395,000,000
Stock Repurchased During Period, Shares					0			9,000,000
Stock Repurchased During Period, Value					(18,000,000)
Cash dividends on common stock					(870,000,000)	(837,000,000)
Other					0	(2,000,000)
Ending Balance	18,796,000,000		18,831,000,000		18,796,000,000	18,831,000,000		19,004,000,000
Stock Issued During Period, Value, Employee Stock Purchase Plan					430,000,000
Number of Common shares Issued [Member]
Changes in Stockholders' Equity
Beginning Balance, Shares					877,803,000	865,664,000		865,664,000
Stock issued, shares					6,144,000	9,697,000
Stock Repurchased During Period, Shares					0
Ending Balance, Shares	883,947,000		875,361,000		883,947,000	875,361,000
Number of Common shares Treasury [Member]
Changes in Stockholders' Equity
Beginning Balance, Shares					10,035,000	539,000		539,000
Stock Repurchased During Period, Shares					0
Other, Shares					9,000	26,000
Ending Balance, Shares	10,044,000		565,000		10,044,000	565,000
Common Stockholders' Equity [Member]
Changes in Stockholders' Equity
Beginning Balance					18,297,000,000	17,578,000,000		17,578,000,000
Net Income After Dividends on Preferred and Preference Stock					378,000,000	991,000,000
Other comprehensive income (loss)					9,000,000	(1,000,000)
Stock issued					244,000,000	395,000,000
Stock Repurchased During Period, Value					(18,000,000)
Cash dividends on common stock					(870,000,000)	(837,000,000)
Other					0	(2,000,000)
Ending Balance	18,040,000,000		18,124,000,000		18,040,000,000	18,124,000,000
Preferred and Preference Stock of Subsidiaries [Member]
Changes in Stockholders' Equity
Beginning Balance					707,000,000	707,000,000		707,000,000
Net Income After Dividends on Preferred and Preference Stock					0	0
Other comprehensive income (loss)					0	0
Stock issued					49,000,000	0
Stock Repurchased During Period, Value					0
Cash dividends on common stock					0	0
Other					0	0
Ending Balance	$ 756,000,000		$ 707,000,000		$ 756,000,000	$ 707,000,000

[1] After dividends on preferred and preference stock of subsidiaries.

[2] Segment net income (loss) for the three months ended June 30, 2013 includes a $450 million pre-tax charge ($277.9 million after tax) for an estimated probable loss on the Kemper IGCC. See Note (B) under "Integrated Coal Gasification Combined Cycle – Kemper IGCC Cost Estimate" herein for additional information.