Derivatives - Balances of outstanding derivative instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Total derivative assets	$ 5	$ 21
LIABILITIES
Total derivative liabilities	0	18
Not designated as hedging instruments
ASSETS
Gross Assets, Subject to master netting arrangements		33
Gross Assets, Not subject to master netting arrangements		19
Gross Assets, Total		52
Offsetting Payables		(66)
Cash Collateral Paid (Received)		35
Net Amount, Derivative assets subject to netting		2
Total derivative assets		21
LIABILITIES
Gross Liabilities, Subject to master netting arrangements		69
Gross Liabilities, Total		69
Offsetting Receivables		(66)
Cash Collateral Received		15
Net Amount, Derivative liabilities subject to netting		18
Total derivative liabilities		18
Not designated as hedging instruments | Forward delivery commitments
ASSETS
Gross Assets, Subject to master netting arrangements		13
Gross Assets, Not subject to master netting arrangements		1
Offsetting Payables		(43)
Cash Collateral Paid (Received)		31
Net Amount, Derivative assets subject to netting		1
LIABILITIES
Gross Liabilities, Subject to master netting arrangements		4
Offsetting Receivables		(10)
Cash Collateral Received		11
Net Amount, Derivative liabilities subject to netting		5
Not designated as hedging instruments | MSR-related agreements
ASSETS
Gross Assets, Subject to master netting arrangements		19
Offsetting Payables		(22)
Cash Collateral Paid (Received)		4
Net Amount, Derivative assets subject to netting		1
LIABILITIES
Gross Liabilities, Subject to master netting arrangements		65
Offsetting Receivables		(55)
Cash Collateral Received		2
Net Amount, Derivative liabilities subject to netting		12
Not designated as hedging instruments | Option contracts
ASSETS
Gross Assets, Subject to master netting arrangements		1
Offsetting Payables		(1)
Cash Collateral Paid (Received)		0
Net Amount, Derivative assets subject to netting		0
LIABILITIES
Gross Liabilities, Subject to master netting arrangements		0
Offsetting Receivables		(1)
Cash Collateral Received		2
Net Amount, Derivative liabilities subject to netting		1
Not designated as hedging instruments | Interest rate lock commitments expected to close
ASSETS
Gross Assets, Not subject to master netting arrangements	$ 5	$ 18