Investment Securities - Gross Unrealized Losses and Fair Value of Company's Investment Securities (Detail) $ in Millions	Jun. 30, 2016 USD ($)
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	$ 3,050
Unrealized Losses Less Than 12 Months	(6)
Fair Value 12 Months or Greater	2,803
Unrealized Losses 12 Months or Greater	(21)
Fair Value Total	5,853
Unrealized Losses Total	(27)
Fair Value Less Than 12 Months	8,427
Unrealized Losses Less Than 12 Months	(34)
Fair Value 12 Months or Greater	4,541
Unrealized Losses 12 Months or Greater	(108)
Fair Value Total	12,968
Unrealized Losses Total	(142)
Mortgage-Backed Securities Residential [Member] \| Agency [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	3,050
Unrealized Losses Less Than 12 Months	(6)
Fair Value 12 Months or Greater	2,778
Unrealized Losses 12 Months or Greater	(19)
Fair Value Total	5,828
Unrealized Losses Total	(25)
Fair Value Less Than 12 Months	8,348
Unrealized Losses Less Than 12 Months	(33)
Fair Value 12 Months or Greater	3,998
Unrealized Losses 12 Months or Greater	(24)
Fair Value Total	12,346
Unrealized Losses Total	(57)
Mortgage-Backed Securities Residential [Member] \| Non-Agency Prime [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	51
Fair Value 12 Months or Greater	95
Unrealized Losses 12 Months or Greater	(4)
Fair Value Total	146
Unrealized Losses Total	(4)
Mortgage-Backed Securities Residential [Member] \| Non-Agency Non-Prime [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	20
Unrealized Losses Less Than 12 Months	(1)
Fair Value 12 Months or Greater	12
Unrealized Losses 12 Months or Greater	(3)
Fair Value Total	32
Unrealized Losses Total	(4)
Asset-Backed Securities [Member] \| Asset-Backed Securities Other [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value 12 Months or Greater	5
Fair Value Total	5
Fair Value 12 Months or Greater	2
Fair Value Total	2
Obligations of State and Political Subdivisions [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value 12 Months or Greater	2
Unrealized Losses 12 Months or Greater	(1)
Fair Value Total	2
Unrealized Losses Total	(1)
Fair Value Less Than 12 Months	7
Fair Value 12 Months or Greater	16
Fair Value Total	23
Other Debt Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value 12 Months or Greater	18
Unrealized Losses 12 Months or Greater	(1)
Fair Value Total	18
Unrealized Losses Total	(1)
Corporate Debt Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value 12 Months or Greater	418
Unrealized Losses 12 Months or Greater	(77)
Fair Value Total	418
Unrealized Losses Total	(77)
Other Investment [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	1
Fair Value Total	$ 1

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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This item represents the fair value of securities categorized as held-to-maturity that have been in a continuous unrealized loss position for less than twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 6
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-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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