Earnings Per Share - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Maximum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Participating securities outstanding	0	1	0	1
Stock and Performance Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Participating securities outstanding, nonforfeitable	17	12	17	12
Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares that would have been included in diluted earnings per share calculation	89	89
Number of anti-dilutive securities	89	89	89	89
Stock Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares that would have been included in diluted earnings per share calculation	17	12
Number of anti-dilutive securities	8	6
Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares that would have been included in diluted earnings per share calculation	9	19
Number of anti-dilutive securities	1	4
Weighted average exercise price of options			10.77	15.44
Equity Unit Purchase Agreements [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities			48	28