Investments in Securities Available-for-sale Securities 3 (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	$ (6)	$ (4)
Less than 12 Consecutive Months, Fair Value	343	339
12 Consecutive Months or Longer, Gross Unrealized Losses	(32)	(203)
12 Consecutive Months or Longer, Fair Value	825	2,375
Fannie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(2)	0
Less than 12 Consecutive Months, Fair Value	188	113
12 Consecutive Months or Longer, Gross Unrealized Losses	(13)	(19)
12 Consecutive Months or Longer, Fair Value	525	627
Alt-A private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(2)	(2)
Less than 12 Consecutive Months, Fair Value	100	171
12 Consecutive Months or Longer, Gross Unrealized Losses	(2)	(13)
12 Consecutive Months or Longer, Fair Value	30	112
Subprime private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	0	0
Less than 12 Consecutive Months, Fair Value	0	0
12 Consecutive Months or Longer, Gross Unrealized Losses	(9)	(24)
12 Consecutive Months or Longer, Fair Value	184	460
Mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(2)	(2)
Less than 12 Consecutive Months, Fair Value	55	47
12 Consecutive Months or Longer, Gross Unrealized Losses	(8)	(11)
12 Consecutive Months or Longer, Fair Value	86	155
Other mortgage-related securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses		0
Less than 12 Consecutive Months, Fair Value		8
12 Consecutive Months or Longer, Gross Unrealized Losses		(136)
12 Consecutive Months or Longer, Fair Value		$ 1,021

Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for securities which are categorized neither as held-to-maturity nor trading securities.

No definition available.

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- Definition

Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for securities categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities 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

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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