Debt and Borrowing Arrangements - Components of Net interest expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Debt Disclosure [Abstract]
Interest income	$ 4	$ 7	$ 7	$ 13
Secured interest expense	(2)	(3)	(4)	(7)
MSRs secured interest expense	(13)	(1)	(27)	(1)
Unsecured interest expense	0	(9)	(1)	(19)
Net interest expense	$ (11)	$ (6)	$ (25)	$ (14)