Reclassification Out of Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic pension cost	$ 8		$ 13		$ 17
Income Before Income Taxes	2,028		2,598		2,210
Applicable income tax expense	545		772		636
Net income	1,481		1,836		1,576
Total reclassifications for the period
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Net income	45	[1]	15	[1]
Net unrealized gains on available-for-sale securities
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment for net losses (gains) included in net income	37	[1]	(6)	[1]	15
Income Before Income Taxes	37	[1]	(6)	[1]
Applicable income tax expense	(13)	[1]	2	[1]
Net income	24	[1]	(4)	[1]
Net unrealized gains on cash flow hedge derivatives
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	44		44		83
Income Before Income Taxes	44	[1]	44	[1]
Applicable income tax expense	(15)	[1]	(15)	[1]
Net income	29	[1]	29	[1]
Net unrealized gains on cash flow hedge derivatives | Interest rate contracts related to C&I loans
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	44	[1]	45	[1]
Net unrealized gains on cash flow hedge derivatives | Interest rate contracts related to long-term debt
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income			(1)	[1]
Amortization of defined periodic benefit costs
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Income Before Income Taxes	(12)	[1]	(16)	[1]
Applicable income tax expense	4	[1]	6	[1]
Net income	(8)	[1]	(10)	[1]
Amortization of defined periodic benefit costs | Amortization of net actuarial (loss) gain
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic pension cost	(7)	[2]	(11)	[2]
Amortization of defined periodic benefit costs | Pension Settlement
Reclassifications Out Of Accumulated Other Comprehensive Income [Line Items]
Net periodic pension cost	$ (5)	[2]	$ (5)	[2]

[1] Amounts in parentheses indicate reductions to net income.

[2] This AOCI component is included in the computation of net periodic benefit cost. Refer to Note 21 for information on the computation of net periodic benefit cost.