Variable Interest Entities (Narrative) (Detail) $ in Billions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Variable Interest Entity [Line Items]
Carrying amounts of assets	$ 2.7	$ 5.4
Carrying amounts of liabilities	$ 2.2	$ 5.1
Number of variable interest entities consolidated	1	1