Exit Costs - Summary of expenses incurred to date by segment (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	$ 0		$ 4	$ 0	$ 13
Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	$ 2		2
Cumulative costs recognized in prior years						$ 35
Estimate of remaining costs	1			1
Program expected costs	38			38
Continuing Operations | Operating segment | Mortgage Servicing Segment | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	0		0
Cumulative costs recognized in prior years						2
Estimate of remaining costs	0			0
Program expected costs	2			2
Continuing Operations | Other | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	0		0
Cumulative costs recognized in prior years						11
Estimate of remaining costs	0			0
Program expected costs	11			11
Discontinued Operations | Other | Reorganization
Restructuring Cost and Reserve [Line Items]
Costs incurred in current year	0	$ 2		2
Cumulative costs recognized in prior years						$ 22
Estimate of remaining costs	1			1
Program expected costs	$ 25			$ 25