Summary of Characteristics of Interest Rate Swaps (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Derivative Instruments:
Weighted Average Pay Rate	2.16%		2.14%
Weighted Average Receive Rate	0.19%		0.20%
Interest Rate Swaps
Derivative Instruments:
Current Notional	$ 56,709,750	[1]	$ 52,426,910	[1]
Weighted Average Pay Rate	2.16%	[2],[3]	2.14%	[2],[3]
Weighted Average Receive Rate	0.19%	[3],[4]	0.20%	[3],[4]
Average Years to Maturity	5 years 3 months 22 days	[3]	5 years 3 months 4 days	[3]
Interest Rate Swaps | 0 - 3 years
Derivative Instruments:
Derivative Instruments minimum maturity period	0 years		0 years
Derivative Instruments maximum maturity period	3 years		3 years
Current Notional	24,516,550	[1]	24,286,000	[1]
Weighted Average Pay Rate	1.78%	[2],[3]	1.83%	[2],[3]
Weighted Average Receive Rate	0.17%	[3],[4]	0.18%	[3],[4]
Average Years to Maturity	1 year 10 months 2 days	[3]	1 year 11 months 23 days	[3]
Interest Rate Swaps | 3 - 6 years
Derivative Instruments:
Derivative Instruments minimum maturity period	3 years		3 years
Derivative Instruments maximum maturity period	6 years		6 years
Current Notional	8,723,500	[1]	8,865,410	[1]
Weighted Average Pay Rate	2.07%	[2],[3]	2.02%	[2],[3]
Weighted Average Receive Rate	0.19%	[3],[4]	0.19%	[3],[4]
Average Years to Maturity	4 years 7 months 6 days	[3]	4 years 2 months 9 days	[3]
Interest Rate Swaps | 6 - 10 years
Derivative Instruments:
Derivative Instruments minimum maturity period	6 years		6 years
Derivative Instruments maximum maturity period	10 years		10 years
Current Notional	17,179,700	[1]	15,785,500	[1]
Weighted Average Pay Rate	2.49%	[2],[3]	2.37%	[2],[3]
Weighted Average Receive Rate	0.23%	[3],[4]	0.23%	[3],[4]
Average Years to Maturity	7 years 9 months 29 days	[3]	7 years 7 months 28 days	[3]
Interest Rate Swaps | Greater than 10 years
Derivative Instruments:
Derivative Instruments minimum maturity period	10 years		10 years
Current Notional	$ 6,290,000	[1]	$ 3,490,000	[1]
Weighted Average Pay Rate	3.66%	[2],[3]	3.62%	[2],[3]
Weighted Average Receive Rate	0.18%	[3],[4]	0.20%	[3],[4]
Average Years to Maturity	21 years 1 month 2 days	[3]	19 years 11 months 5 days	[3]

[1] Notional amount includes $3.1 billion in forward starting pay fixed swaps, offset by $1.4 billion in forward starting receive fixed swaps.

[2] Weighted average fixed rate on forward starting pay fixed swaps was 3.00%

[3] Excludes forward starting swaps.

[4] Weighted average fixed rate on forward starting pay receive swaps was 1.81%