Contingencies - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended
	Jul. 25, 2014	Mar. 31, 2016	Sep. 30, 2014	Jun. 30, 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
Total Cash Payment for Settlement [Domain] | Mortgage Modification Investigation and HAMP [Member]
Loss Contingency, Damages Awarded, Value			$ 46
Consumer Remediation [Member] | Mortgage Modification Investigation and HAMP [Member]
Loss Contingency, Damages Awarded, Value			179
Cash payment for litigation [Member] | Potential Mortgage Servicing Settlement and Claims [Member]
Loss Contingency, Damages Awarded, Value		50
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
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