Fair Value Measurements - Schedule of assets and liabilities measured at fair value on a recurring basis (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value Measurements
Mortgage servicing rights	$ 476	$ 690
Total derivative assets	5	21
Total derivative liabilities	0	18
Liability to deliver MSRs	2	0
Recurring basis | Forward delivery commitments
Fair Value Measurements
Other assets—Derivative assets, Cash Collateral and Netting		(12)
Other liabilities-derivative liabilities, Cash Collateral and Netting		1
Recurring basis | MSR-related agreements
Fair Value Measurements
Other assets—Derivative assets, Cash Collateral and Netting		(18)
Other liabilities-derivative liabilities, Cash Collateral and Netting		(53)
Recurring basis | Option contracts
Fair Value Measurements
Other assets—Derivative assets, Cash Collateral and Netting		(1)
Other liabilities-derivative liabilities, Cash Collateral and Netting		1
Recurring basis | Level One
Fair Value Measurements
Mortgage loans held for sale	0	0
Mortgage servicing rights	0	0
Mortgage servicing rights secured liability	0
Liability to deliver MSRs	0
Recurring basis | Level One | Interest rate lock commitments expected to close
Fair Value Measurements
Other assets—Derivative assets	0	0
Recurring basis | Level One | Forward delivery commitments
Fair Value Measurements
Other assets—Derivative assets		0
Other liabilities-derivative liabilities		0
Recurring basis | Level One | MSR-related agreements
Fair Value Measurements
Other assets—Derivative assets		0
Other liabilities-derivative liabilities		0
Recurring basis | Level One | Option contracts
Fair Value Measurements
Other assets—Derivative assets		0
Other liabilities-derivative liabilities		0
Recurring basis | Level Two
Fair Value Measurements
Mortgage loans held for sale	261	636
Mortgage servicing rights	0	0
Mortgage servicing rights secured liability	0
Liability to deliver MSRs	0
Recurring basis | Level Two | Interest rate lock commitments expected to close
Fair Value Measurements
Other assets—Derivative assets	0	0
Recurring basis | Level Two | Forward delivery commitments
Fair Value Measurements
Other assets—Derivative assets		14
Other liabilities-derivative liabilities		4
Recurring basis | Level Two | MSR-related agreements
Fair Value Measurements
Other assets—Derivative assets		19
Other liabilities-derivative liabilities		65
Recurring basis | Level Two | Option contracts
Fair Value Measurements
Other assets—Derivative assets		1
Other liabilities-derivative liabilities		0
Recurring basis | Level Three
Fair Value Measurements
Mortgage loans held for sale	9	47
Mortgage servicing rights		690
Mortgage servicing rights secured liability	419
Liability to deliver MSRs	2
Recurring basis | Level Three | Interest rate lock commitments expected to close
Fair Value Measurements
Other assets—Derivative assets	5	18
Recurring basis | Level Three | Forward delivery commitments
Fair Value Measurements
Other assets—Derivative assets		0
Other liabilities-derivative liabilities		0
Recurring basis | Level Three | MSR-related agreements
Fair Value Measurements
Other assets—Derivative assets		0
Other liabilities-derivative liabilities		0
Recurring basis | Level Three | Option contracts
Fair Value Measurements
Other assets—Derivative assets		0
Other liabilities-derivative liabilities		0
Total | Recurring basis
Fair Value Measurements
Mortgage loans held for sale	270	683
Mortgage servicing rights	476	690
Mortgage servicing rights secured liability	419
Liability to deliver MSRs	2
Total | Recurring basis | Interest rate lock commitments expected to close
Fair Value Measurements
Total derivative assets	$ 5	18
Total | Recurring basis | Forward delivery commitments
Fair Value Measurements
Total derivative assets		2
Total derivative liabilities		5
Total | Recurring basis | MSR-related agreements
Fair Value Measurements
Total derivative assets		1
Total derivative liabilities		12
Total | Recurring basis | Option contracts
Fair Value Measurements
Total derivative assets		0
Total derivative liabilities		$ 1