Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) (Fixed Rate Long-Term Borrowings [Member], Fair Value Hedges [Member], USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Fixed Rate Long-Term Borrowings [Member] | Fair Value Hedges [Member]
Derivative [Line Items]
Notional Amount	$ 1,400,000,000	$ 1,400,000,000
Average Maturity (in years)	2 years 4 months 24 days	2 years 8 months 12 days
Weighted-Average Rate, Fixed	4.42%	4.42%
Weighted-Average Rate, Variable	1.22%	1.19%