Tangible Equity Units - Settlement Rate Scenarios for Equity Component (Detail) - 7.50% Tangible Equity Units [Member]	Sep. 30, 2015 $ / shares
Threshold Appreciation Price [Member]
Tangible Equity Units [Line Items]
Equity component applicable market value	$ 69.8422
Reference Price [Member]
Tangible Equity Units [Line Items]
Equity component applicable market value	$ 58.20
Exceeds Threshold Appreciation Price [Member] | Settled In WGP Shares [Member]
Tangible Equity Units [Line Items]
Minimum settlement rate	0.7159
Less Than Reference Price [Member] | Settled In WGP Shares [Member]
Tangible Equity Units [Line Items]
Maximum settlement rate	0.8591