Income Taxes (Summary of Tax Credits and NOL Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Investment Tax Credits [Member]
Investment Tax Credits	$ 362
Expiration year	2029 – 2031
Alternative Minimum Tax Credits [Member]
Alternative Minimum Tax Credits	145
Expiration year	Indefinite
Federal [Member]
Operating Loss Carryforwards	274
Expiration year	2031
State [Member]
Operating Loss Carryforwards	47	[1]
Expiration year	2016 – 2031	[1]
Foreign [Member]
Operating Loss Carryforwards	$ 102	[2]
Expiration year	2015 – 2029; Indefinite	[2]

[1] A valuation allowance of $41 million has been recorded on the State NOL Carryforwards, as presented in the Net Deferred Income Tax Liability Components table.

[2] A valuation allowance of $102 million has been recorded on the Foreign NOL Carryforwards, as presented in the Net Deferred Income Tax Liability Components table.