Fair Value Measurements - Quantitative Information about Nonrecurring Fair Value Measurement of Assets and Liabilities Classified as Level 3 (Detail) (Level 3 [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	58		164
Residential Mortgage [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	5	[1]	56	[1]
Impaired commercial loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	53	[2]	108	[2]
Fair Value, Measurements, Nonrecurring [Member] | Residential Mortgage [Member] | Minimum [Member] | Third Party Appraisal [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Fair Value Inputs, Loss Severity	0.00%		0.00%
Fair Value, Measurements, Nonrecurring [Member] | Residential Mortgage [Member] | Maximum [Member] | Third Party Appraisal [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Fair Value Inputs, Loss Severity	100.00%		100.00%
Fair Value, Measurements, Nonrecurring [Member] | Impaired commercial loans [Member] | Minimum [Member] | Third Party Appraisal [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Fair Value Inputs, Loss Severity	8.00%		1.00%
Fair Value, Measurements, Nonrecurring [Member] | Impaired commercial loans [Member] | Maximum [Member] | Third Party Appraisal [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Fair Value Inputs, Loss Severity	47.00%		66.00%

[1] As of December 31, 2014 and 2013, the fair value of the loans held for sale was below cost. Certain residential mortgage loans held for sale have been classified as a Level 3 fair value measurement within the fair value hierarchy as the underlying real estate properties which determine fair value are illiquid assets as a result of market conditions and significant inputs in estimating fair value were unobservable. Additionally, the fair value of these properties is affected by, among other things, the location, the payment history and the completeness of the loan documentation.

[2] Certain commercial loans have undergone troubled debt restructurings and are considered impaired. As a matter of practical expedient, we measure the credit impairment of a collateral-dependent loan based on the fair value of the collateral asset. The collateral often involves real estate properties that are illiquid due to market conditions. As a result, these loans are classified as a Level 3 fair value measurement within the fair value hierarchy.