Investments in Securities Available-for-sale Securities 3 (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	$ (111)	$ (223)
Less than 12 Consecutive Months, Fair Value	2,089	3,580
12 Consecutive Months or Longer, Gross Unrealized Losses	(484)	(660)
12 Consecutive Months or Longer, Fair Value	3,328	3,802
Fannie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(36)	(40)
Less than 12 Consecutive Months, Fair Value	825	975
12 Consecutive Months or Longer, Gross Unrealized Losses	(5)	(4)
12 Consecutive Months or Longer, Fair Value	94	126
Alt-A private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(4)	(12)
Less than 12 Consecutive Months, Fair Value	216	490
12 Consecutive Months or Longer, Gross Unrealized Losses	(17)	(30)
12 Consecutive Months or Longer, Fair Value	206	308
Subprime private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(21)	(24)
Less than 12 Consecutive Months, Fair Value	299	448
12 Consecutive Months or Longer, Gross Unrealized Losses	(65)	(131)
12 Consecutive Months or Longer, Fair Value	928	1,332
Mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(50)	(147)
Less than 12 Consecutive Months, Fair Value	749	1,662
12 Consecutive Months or Longer, Gross Unrealized Losses	(204)	(277)
12 Consecutive Months or Longer, Fair Value	1,040	970
Other mortgage-related 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	5
12 Consecutive Months or Longer, Gross Unrealized Losses	(193)	(218)
12 Consecutive Months or Longer, Fair Value	$ 1,060	$ 1,066