Schedule I - Condensed Financial Information Of Parent Company (Balance Sheets) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
CURRENT ASSETS
Cash and cash equivalents	$ 25	$ 109	$ 21	$ 46
Prepayments of income taxes	59	74
Total Current Assets	1,249	1,439
Investments and Other Assets
Goodwill	1,407	1,407	1,407
Other	163	163
Total Investments and Other Assets	5,681	5,251
Total Assets	15,776	14,910
CURRENT LIABILITIES
Short-term debt	965	732
Total Current Liabilities	2,527	1,861
Deferred Credits
Liabilities and accrued interest related to uncertain tax positions	15	32
Long-Term Debt	3,648	3,794
Commitments and Contingencies (Note 4)
Equity
Common stock, $.01 par value; authorized 400,000,000 shares; 230,015,427 and 227,500,190 shares outstanding, respectively	2	2
Premium on stock and other capital contributions	3,383	3,325
Accumulated other comprehensive loss	(48)	(63)	(106)	(138)
Retained earnings	1,109	1,072
Total Liabilities and Equity	15,776	14,910
Parent Company [Member]
CURRENT ASSETS
Cash and cash equivalents	262	257	131	585
Prepayments of income taxes	12	51
Accounts receivable and other	7	7
Total Current Assets	281	315
Investments and Other Assets
Goodwill	1,398	1,398
Notes receivable from subsidiary companies		154
Investment in consolidated companies	3,897	3,654
Other	55	24
Total Investments and Other Assets	5,350	5,230
Total Assets	5,631	5,545
CURRENT LIABILITIES
Short-term debt	464	465
Interest and taxes accrued	11	11
Accounts payable due to associated companies	2	25
Total Current Liabilities	477	501
Deferred Credits
Liabilities and accrued interest related to uncertain tax positions	3	3
Long-Term Debt	705	705
Commitments and Contingencies (Note 4)
Equity
Common stock, $.01 par value; authorized 400,000,000 shares; 230,015,427 and 227,500,190 shares outstanding, respectively	2	2
Premium on stock and other capital contributions	3,383	3,325
Accumulated other comprehensive loss	(48)	(63)
Retained earnings	1,109	1,072
Total equity	4,446	4,336
Total Liabilities and Equity	$ 5,631	$ 5,545