Notional Amounts of Swap Agreement, Weighted Average Interest Rates and Remaining Term (Detail) - Interest rate swap agreements - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Notional Amount	$ 1,771,000,000	$ 3,866,000,000
Weighted Average Fixed Rate	1.51%	1.24%
Remaining Term in Months	34 months	32 months
Less than 1 year
Derivative [Line Items]
Notional Amount	$ 500,000,000	$ 950,000,000
Weighted Average Fixed Rate	0.79%	0.68%
Remaining Term in Months	6 months	9 months
1 year to 2 years
Derivative [Line Items]
Notional Amount	$ 410,000,000	$ 930,000,000
Weighted Average Fixed Rate	0.96%	0.96%
Remaining Term in Months	16 months	18 months
2 years to 3 years
Derivative [Line Items]
Notional Amount	$ 150,000,000	$ 1,000,000,000
Weighted Average Fixed Rate	1.29%	1.13%
Remaining Term in Months	34 months	30 months
3 years to 4 years
Derivative [Line Items]
Notional Amount	$ 166,000,000	$ 250,000,000
Weighted Average Fixed Rate	1.45%	1.28%
Remaining Term in Months	46 months	44 months
4 years to 5 years
Derivative [Line Items]
Notional Amount	$ 125,000,000	$ 216,000,000
Weighted Average Fixed Rate	2.44%	1.88%
Remaining Term in Months	57 months	58 months
5 years to 7 years
Derivative [Line Items]
Notional Amount	$ 420,000,000	$ 320,000,000
Weighted Average Fixed Rate	2.73%	2.54%
Remaining Term in Months	75 months	78 months
7 years to 10 years
Derivative [Line Items]
Notional Amount		$ 200,000,000
Weighted Average Fixed Rate		3.00%
Remaining Term in Months	0 months	93 months