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	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	53		58
Residential Mortgage [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	5	[1]	5	[1]
Impaired commercial loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	48	[2]	53	[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	17.00%		8.00%
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	40.00%		47.00%

[1] As of March 31, 2015 and December 31, 2014, 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.