Mortgage Loans Credit Quality Indicators - SF (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 3,047,794	$ 3,064,669
Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	45,300	48,600
Single-Family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,858,561	2,878,691
Single-Family [Member] | Primary [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,656,220	2,649,297
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Less Than or Equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,156,165	2,073,079
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 80% and Less Than or Equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	261,709	276,011
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 90% and Less Than or Equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	140,778	153,474
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 100% and Less Than or Equal to 110% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	43,014	59,630
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 110% and Less Than or Equal to 120% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	23,439	33,954
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 120% and Less Than or Equal to 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	7,529	11,256
Single-Family [Member] | Primary [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	23,586	41,893
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	112,761	127,509
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Less Than or Equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	60,851	61,670
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 80% and Less Than or Equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	15,151	16,794
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 90% and Less Than or Equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	12,490	14,709
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 100% and Less Than or Equal to 110% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	8,998	11,006
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 110% and Less Than or Equal to 120% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	6,033	7,742
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 120% and Less Than or Equal to 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,114	2,951
Single-Family [Member] | Alt-A [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	7,124	12,637
Single-Family [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	44,259	53,291
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Less Than or Equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	22,558	24,112
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 80% and Less Than or Equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	6,046	6,947
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 90% and Less Than or Equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	5,236	6,402
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 100% and Less Than or Equal to 110% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	3,900	5,146
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 110% and Less Than or Equal to 120% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,615	3,691
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 120% and Less Than or Equal to 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	904	1,406
Single-Family [Member] | Other [Member] | Estimated Mark-to-Market Loan-to-Value Ratio Greater Than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	3,000	5,587
Single-Family [Member] | Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 45,321	$ 48,594