Investments in Securities Available-for-sale Securities 3 (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	$ (223)	$ (43)
Less Than 12 Consecutive Months, Fair Value	3,580	1,605
12 Consecutive Moths or Longer, Gross Unrealized Losses	(660)	(2,006)
12 Consecutive Months or Longer, Fair Value	3,802	12,862
Fannie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(40)	(5)
Less Than 12 Consecutive Months, Fair Value	975	599
12 Consecutive Moths or Longer, Gross Unrealized Losses	(4)	(11)
12 Consecutive Months or Longer, Fair Value	126	372
Alt-A private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(12)	(18)
Less Than 12 Consecutive Months, Fair Value	490	541
12 Consecutive Moths or Longer, Gross Unrealized Losses	(30)	(715)
12 Consecutive Months or Longer, Fair Value	308	4,465
Subprime private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(24)	(14)
Less Than 12 Consecutive Months, Fair Value	448	243
12 Consecutive Moths or Longer, Gross Unrealized Losses	(131)	(893)
12 Consecutive Months or Longer, Fair Value	1,332	5,058
CMBS [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		0
12 Consecutive Moths or Longer, Gross Unrealized Losses		(11)
12 Consecutive Months or Longer, Fair Value		240
Mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	(147)	(3)
Less Than 12 Consecutive Months, Fair Value	1,662	127
12 Consecutive Moths or Longer, Gross Unrealized Losses	(277)	(94)
12 Consecutive Months or Longer, Fair Value	970	1,198
Other mortgage-related securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Consecutive Months, Gross Unrealized Losses	0	(3)
Less Than 12 Consecutive Months, Fair Value	5	95
12 Consecutive Moths or Longer, Gross Unrealized Losses	(218)	(282)
12 Consecutive Months or Longer, Fair Value	$ 1,066	$ 1,529