Other Assets - Schedule of Others Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Loans subject to repurchase from Ginnie Mae	$ 774	$ 266
Accrued revenues	155	145
Right-of-use assets	133	0
Intangible assets	116	117
Goodwill	109	23
Other	291	244
Total other assets	$ 1,578	$ 795