Fair Value Level 3 Valuation - Nonrecurring (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	$ 12,057	$ 14,075
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	509	157
Mortgage loans held for investment, at fair value	2,767,813	2,702,526
Total nonrecurring assets at fair value	2,844,940	2,770,088
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	2,751	5,541
Mortgage loans held for investment, at fair value	316,742	351,355
Total nonrecurring assets at fair value	323,739	367,852
Fair Value, Measurements, Nonrecurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	250	17
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	1,088	3,991
Total nonrecurring assets at fair value	5,906	13,934
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Consensus without inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	1,025	3,651
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single vendor without inputs [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	54	336
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for sale, at lower of cost or fair value	9	4
Other assets	$ 12	$ 30
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Accepted Offers [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Number of properties measured	19.00%	18.00%
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Proprietary Home Price Model and Appraisals [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Number of properties measured	75.00%	77.00%
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	$ 1,792	$ 3,211
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	99	134
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Internal model [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	2,816	6,379
Acquired property, net	476	986
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Accepted Offers [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	340	541
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Appraisals [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	571	1,117
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Single-Family [Member] | Walk Forwards [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Acquired property, net	306	433
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	198	323
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member] | Other valuation technique [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	3	5
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member] | Broker Price Opinions [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	25	82
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Multifamily [Member] | Asset Manager Estimate [Member]
Fair Value Inputs, Quantitative Information [Line Items]
Mortgage loans held for investment, at fair value	$ 170	$ 236