Legal Matters - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended	0 Months Ended
	Dec. 31, 2013	Sep. 30, 2013 Class plaintiffs	Jan. 27, 2014 Class plaintiffs Subsequent Event	Dec. 16, 2013 Interchage Litigation
Loss Contingencies [Line Items]
Payments on litigation matters		$ 4,033,000,000
Adjustment to payments for litigation			1,100,000,000
Damages sought by plaintiff from all defendant parties				54,000,000,000
Estimated compensatory damages	$ 145,000,000