Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Minimum [Member]
Aggregate range of reasonably possible losses on legal matters in excess of the accrued liability	$ 0
Maximum [Member]
Aggregate range of reasonably possible losses on legal matters in excess of the accrued liability	180
Mortgage Modification Investigation and HAMP [Member]
Loss Contingency, Damages Awarded, Value	204
Consumer Remediation [Member] | Mortgage Modification Investigation and HAMP [Member]
Loss Contingency, Damages Awarded, Value	179
Consumer Remediation [Member] | Mortgage Modification Investigation and HAMP [Member] | Maximum [Member]
Loss Contingency, Damages Awarded, Value	274
Cash payment for litigation [Member] | Potential Mortgage Servicing Settlement and Claims [Member]
Loss Contingency, Damages Awarded, Value	468
Housing counseling for homeowners [Member] | Mortgage Modification Investigation and HAMP [Member]
Loss Contingency, Damages Awarded, Value	20
Civil money penalty [Member] | Consent Order Foreclosure Actions [Member]
Loss Contingency, Damages Awarded, Value	160
Consumer relief obligation [Member] | Potential Mortgage Servicing Settlement and Claims [Member]
Loss Contingency, Damages Awarded, Value	500
Total Cash Payment for Settlement [Domain] | Mortgage Modification Investigation and HAMP [Member]
Loss Contingency, Damages Awarded, Value	46
Mortgage Modification Investigation and HAMP [Member] | Restitution to Fannie Mae and Freddie Mac [Member]
Loss Contingency, Damages Awarded, Value	10
Mortgage Modification Investigation and HAMP [Member] | Cash payment for litigation [Member]
Loss Contingency, Damages Awarded, Value	$ 16