Fair Value Measurements - Quantitative Information about Nonrecurring Level 3 Fair Value Financial Instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	$ 3,317		$ 3,317		$ 3,732
Total assets at fair value	3,326		3,326		3,742
Net gain (loss) on loan sales	75	$ 63	124	$ 123
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	6		6		5
Repossessed assets	9		9		7
Total assets at fair value	66		66		24
Fair value losses on loans			(1)		(1)
Fair value losses on repossessed assets			(3)		(3)
Net gain (loss) on loan sales			(39)		(8)
Nonrecurring | Residential first mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	14		14		12
Fair value losses on loans			(5)		(4)
Nonrecurring | Commercial and Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	37		37
Fair value losses on loans			(30)
Nonrecurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	6		6		5
Repossessed assets	0		0		0
Total assets at fair value	43		43		5
Nonrecurring | Level 2 | Residential first mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	0		0		0
Nonrecurring | Level 2 | Commercial and Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	37		37
Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale	0		0		0
Repossessed assets	9		9		7
Total assets at fair value	23		23		19
Nonrecurring | Level 3 | Residential first mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	14		14		$ 12
Nonrecurring | Level 3 | Commercial and Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	$ 0		$ 0