Summary of Significant Accounting Policies Narratives(Details) (USD $)	3 Months Ended												12 Months Ended					3 Months Ended				12 Months Ended	3 Months Ended	12 Months Ended	0 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended		36 Months Ended						12 Months Ended				0 Months Ended	3 Months Ended					9 Months Ended	0 Months Ended	12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 contracts	Dec. 31, 2011 contracts	Dec. 31, 2010	Apr. 02, 2013	Dec. 31, 2009	Dec. 31, 2012 Out-of-Period Adjustment [Member]	Sep. 30, 2012 Out-of-Period Adjustment [Member]	Jun. 30, 2012 Out-of-Period Adjustment [Member]	Mar. 31, 2012 Out-of-Period Adjustment [Member]	Dec. 31, 2012 Out-of-Period Adjustment [Member]	Sep. 30, 2012 Loans Discharged with Bankruptcy Relief [Member] Out-of-Period Adjustment [Member]	Dec. 31, 2012 Other Out of Period Adjustments [Member] Out-of-Period Adjustment [Member]	Sep. 07, 2008 US Treasury [Member]	Dec. 31, 2012 US Treasury [Member]	Sep. 30, 2012 US Treasury [Member]	Dec. 31, 2012 US Treasury [Member]	Dec. 31, 2011 US Treasury [Member]	Dec. 31, 2012 US Treasury [Member]	Dec. 31, 2009 US Treasury [Member]	Dec. 31, 2012 US Treasury [Member] Temporary Credit and Liquidity Facilities Program [Member]	Dec. 31, 2011 US Treasury [Member] Temporary Credit and Liquidity Facilities Program [Member]	Dec. 31, 2012 US Treasury [Member] New Issue Bond [Member]	Dec. 31, 2011 US Treasury [Member] New Issue Bond [Member]	Dec. 31, 2012 Freddie Mac [Member]	Dec. 31, 2011 Freddie Mac [Member]	Dec. 31, 2010 Freddie Mac [Member]	Dec. 31, 2010 Ally [Member]	Jan. 31, 2013 GMAC Mortgage LLC [Member]	Sep. 30, 2012 Single-Family Loan Loss Reserve Models Update [Member]	Sep. 30, 2012 Single-Family Collectively Impaired Loan Loss Models Update [Member]	Sep. 30, 2012 Single-Family Individually Impaired Loan Loss Models Update [Member]	Jun. 30, 2012 Net OTTI [Member]	Sep. 30, 2011 TDR Accounting Guidance [Member]	Sep. 30, 2011 TDR Accounting Guidance [Member] contracts	Sep. 08, 2008 Series 2008-2 Senior Preferred Stock [Member]	Dec. 31, 2012 Series 2008-2 Senior Preferred Stock [Member]
Accounting Policies [Abstract]
Number of days of net worth deficit requiring FHFA to place us into receivership	60 days												60 days
Related Parties [Line Items]
Shares of variable liquidation preference senior preferred stock issued																																															1,000,000
Maximum commitment from US Treasury pursuant to the senior preferred stock purchase agreement																															$ 200,000,000,000																$ 100,000,000,000
Total available funding from US Treasury pursuant to the senior preferred stock agreement after 2012																										117,600,000,000		117,600,000,000		117,600,000,000	124,800,000,000
Net worth	7,224,000,000								(4,571,000,000)				7,224,000,000	(4,571,000,000)	(2,517,000,000)		(11,983,000,000)
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement during period																														40,900,000,000
Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement																116,100,000,000										116,100,000,000		116,100,000,000		116,100,000,000
Initial aggregate liquidation preference of senior preferred stock held by US Treasury																										1,000,000,000		1,000,000,000		1,000,000,000
Aggregate liquidation preference of senior preferred stock																										117,100,000,000		117,100,000,000		117,100,000,000																	1,000,000,000
Senior preferred stock annual dividend rate																												10.00%																				10.00%	[1]
Capital reserve amount for the next fiscal year based on the amended Senior Preferred Stock Purchase agreement	3,000,000,000												3,000,000,000													3,000,000,000		3,000,000,000		3,000,000,000
Annual reduction of capital reserve from 2013 to 2018 based on the Senior Preferred Stock Purchase Agreement, Amendment	600,000,000												600,000,000													600,000,000		600,000,000		600,000,000
Percentage of common shares attributable to warrants issued to Treasury as a percentage to total diluted common shares upon exercise of the right	79.90%												79.90%												79.90%	79.90%		79.90%		79.90%
Common stock warrant exercise price per share																									0.00001
Fair value of the warrant at issuance																									3,500,000,000
Home Affordable Modification Program administrative expense reimbursements													96,000,000	106,000,000	167,000,000
Proceeds from income tax refunds														1,100,000,000															1,100,000,000
Income tax benefit recognized from our settlement of 2007 and 2008 tax years with the IRS																													90,000,000
Principal and interest outstanding																																1,600,000,000	3,000,000,000	6,100,000,000	7,500,000,000
Percentage of initial principal loss US Treasury will bear for Temporary Credit and Liquidity Facilities and New Issue Bond Programs																										35.00%		35.00%		35.00%
Loss of principal or interest under Treasury's Temporary Credit and Liquid Facilities and New Issue Bond Programs																										0		0		0
Increase of guarantee fee rate resulting from the Temporary Payroll Tax Cut Continuation Act of 2011.																										0.10%		0.10%		0.10%
TCCA guaranty fee																										134,000,000		238,000,000
TCCA guaranty fee remitted																											104,000,000
Fair value of mortgage-backed securities																																				12,200,000,000	15,600,000,000
Interest receivable	9,176,000,000								10,000,000,000				9,176,000,000	10,000,000,000																						51,000,000	69,000,000
Investment income, interest																																				551,000,000	700,000,000	1,100,000,000
Amount received in exchange for our release of specified Ally affiliates from certain potential liability																																							462,000,000	265,000,000
Increase of provision (increase of benefit) for credit losses	(1,890,000,000)	[2]	2,079,000,000	[2]	(3,041,000,000)	[2]	2,000,000,000	[2]	5,476,000,000	4,151,000,000	6,537,000,000	10,554,000,000	(852,000,000)	26,718,000,000	24,896,000,000			172,000,000	850,000,000	503,000,000	548,000,000	2,100,000,000	850,000,000	1,200,000,000																(173,000,000)
Change in Accounting Estimate [Abstract]
Increase (decrease) to the allowance for loan losses and provision for credit losses																																									3,500,000,000	(1,500,000,000)	5,000,000,000		514,000,000
Increase in other-than-temporary impairment expense due to change in assumptions used to project cash flow estimate on Alt-A and subprime private-label securities																																												500,000,000
Number of loans troubled debt restructurings activity													337,409	208,911																																22,000
Maximum term of early lender funding advances													60 days
Securities Received as Collateral [Abstract]
Collateral held on reverse repurchase agreements	45,800,000,000								49,500,000,000				45,800,000,000	49,500,000,000
Fair value of non-cash collateral	46,200,000,000								50,100,000,000				46,200,000,000	50,100,000,000
Fair value of non-cash collateral that can be sold or repledged	25,000,000,000								20,000,000,000				25,000,000,000	20,000,000,000
Fair value of securities received as collateral that have been sold or repledged	$ 0								$ 0				$ 0	$ 0

[1] Rate effective September 9, 2008 through December 31, 2012.

[2] Includes out-of-period adjustments of $548 million, $503 million, $850 million, and $172 million which increased our provision for credit losses for the three months ended March 31, 2012, June 30, 2012, September 30, 2012, and December 31, 2012, respectively.