Schedule I - Condensed Financial Information of Parent Company (Balance Sheets) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CURRENT ASSETS
Cash and cash equivalents	$ 14	$ 23	$ 25	$ 109
Total Current Assets	1,084	1,398
INVESTMENTS AND OTHER ASSETS
Goodwill	1,407	1,407
Other	166	163
TOTAL ASSETS	15,667	14,848	14,519
CURRENT LIABILITIES
Short-term debt	729	565
Current portion of long-term debt	431	446
Total Current Liabilities	2,065	2,313
DEFERRED CREDITS
Liabilities and accrued interest related to uncertain tax positions	2	28
Long-term debt	4,441	4,053
COMMITMENTS AND CONTINGENCIES (NOTE 4)
PREFERRED STOCK
Series A preferred stock, $.01 par value, 18,000 shares authorized, 12,600 and zero shares outstanding, respectively	129
EQUITY
Common stock	3	3
Premium on stock and other capital contributions	3,800	3,751
Accumulated other comprehensive loss	(46)	(34)	(48)	(63)
Retained earnings	565	595
TOTAL LIABILITIES AND EQUITY	15,667	14,848
Parent Company [Member]
CURRENT ASSETS
Cash and cash equivalents	65		262	257
Prepayments of income taxes	152	151
Accounts receivable and other	9	28
Total Current Assets	226	179
INVESTMENTS AND OTHER ASSETS
Goodwill	1,398	1,398
Investment in consolidated companies	4,256	3,935
Other	84	37
Total Investments and Other Assets	5,738	5,370
TOTAL ASSETS	5,964	5,549
CURRENT LIABILITIES
Short-term debt	287	24
Current portion of long-term debt	250
Interest and taxes accrued	9	10
Accounts payable due to associated companies	13	1
Total Current Liabilities	559	35
DEFERRED CREDITS
Notes payable due to subsidiary companies	494	491
Liabilities and accrued interest related to uncertain tax positions	4	3
Total Deferred Credits	498	494
Long-term debt	456	705
COMMITMENTS AND CONTINGENCIES (NOTE 4)
PREFERRED STOCK
Series A preferred stock, $.01 par value, 18,000 shares authorized, 12,600 and zero shares outstanding, respectively	129
EQUITY
Common stock	3	3
Premium on stock and other capital contributions	3,800	3,751
Accumulated other comprehensive loss	(46)	(34)
Retained earnings	565	595
Total Equity	4,322	4,315
TOTAL LIABILITIES AND EQUITY	$ 5,964	$ 5,549