Fair Value Election and Measurement Level 3 Significant Unobservable Input Assumptions (Details) - USD ($) $ in Millions		6 Months Ended		12 Months Ended
		Jun. 30, 2018		Dec. 31, 2017
level 3 fair value assumptions [Line Items]
Available-for-sale Securities	[1],[2]	$ 30,942		$ 30,947	[3]
Loans Receivable, Fair Value Disclosure		177		196
Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Available-for-sale Securities		0		72
Loans Receivable, Fair Value Disclosure		177		196
Fair Value, Measurements, Recurring [Member]
level 3 fair value assumptions [Line Items]
Available-for-sale Securities		30,942	[4]	30,947	[5]
Loans Receivable, Fair Value Disclosure		177		196
Servicing Asset at Fair Value, Amount		1,959		1,710
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Available-for-sale Securities		0	[4]	72	[5]
Loans Receivable, Fair Value Disclosure		177		196
Servicing Asset at Fair Value, Amount		1,959		1,710
Fair Value, Measurements, Recurring [Member] | Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Derivative, Fair Value, Net		3	[6]	0	[7]
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member] | Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Available-for-sale Securities				8
Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member] | Cost Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Available-for-sale Securities				5
Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member] | Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Available-for-sale Securities				59
Fair Value, Measurements, Recurring [Member] | Loans Held-For-Investment [Member] | Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Loans Receivable, Fair Value Disclosure		5		4
Fair Value, Measurements, Recurring [Member] | Loans Held-For-Investment [Member] | Income Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Loans Receivable, Fair Value Disclosure		$ 172		$ 192
Fair Value, Measurements, Recurring [Member] | Loans Held-For-Investment [Member] | Income Approach Valuation Technique [Member] | Minimum [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Fair Value Inputs, Option Adjusted Spread		0.62%		0.62%
Fair Value Inputs, Prepayment Rate		7.00%		2.00%
Fair Value Inputs, Probability of Default		0.00%		0.00%
Fair Value, Measurements, Recurring [Member] | Loans Held-For-Investment [Member] | Income Approach Valuation Technique [Member] | Maximum [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Fair Value Inputs, Option Adjusted Spread		7.84%		7.84%
Fair Value Inputs, Prepayment Rate		28.00%		34.00%
Fair Value Inputs, Probability of Default		2.00%		5.00%
Fair Value, Measurements, Recurring [Member] | Loans Held-For-Investment [Member] | Income Approach Valuation Technique [Member] | Weighted Average [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Fair Value Inputs, Option Adjusted Spread		1.76%		2.15%
Fair Value Inputs, Prepayment Rate		13.00%		11.00%
Fair Value Inputs, Probability of Default		0.70%		0.67%
Fair Value, Measurements, Recurring [Member] | Mortgage Servicing Rights [Member] | Income Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Servicing Asset at Fair Value, Amount		$ 1,959		$ 1,710
Fair Value, Measurements, Recurring [Member] | Mortgage Servicing Rights [Member] | Income Approach Valuation Technique [Member] | Minimum [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Fair Value Inputs, Option Adjusted Spread		0.00%		1.00%
Fair Value Inputs, Prepayment Rate		6.00%		6.00%
Fair Value, Measurements, Recurring [Member] | Mortgage Servicing Rights [Member] | Income Approach Valuation Technique [Member] | Maximum [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Fair Value Inputs, Option Adjusted Spread		117.00%		125.00%
Fair Value Inputs, Prepayment Rate		30.00%		30.00%
Fair Value, Measurements, Recurring [Member] | Mortgage Servicing Rights [Member] | Income Approach Valuation Technique [Member] | Weighted Average [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Fair Value Inputs, Option Adjusted Spread		3.00%		4.00%
Fair Value Inputs, Prepayment Rate		13.00%		13.00%
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Market Approach Valuation Technique [Member] | Minimum [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Fair Value Inputs, Pull Through Rate		41.00%		41.00%
Fair Value Inputs, Msr Value		0.33%		0.41%
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Market Approach Valuation Technique [Member] | Maximum [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Fair Value Inputs, Pull Through Rate		100.00%		100.00%
Fair Value Inputs, Msr Value		1.90%		1.90%
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Market Approach Valuation Technique [Member] | Weighted Average [Member] | Fair Value, Inputs, Level 3 [Member]
level 3 fair value assumptions [Line Items]
Fair Value Inputs, Pull Through Rate		80.00%		81.00%
Fair Value Inputs, Msr Value		1.05%		1.13%

[1] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets. Reclassifications have been made to previously reported amounts for comparability.

[2] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $184 million and $223 million at June 30, 2018 and December 31, 2017, respectively.

[3] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets on the Consolidated Balance Sheets. Reclassifications have been made to previously reported amounts for comparability. See Note 9, "Other Assets," for additional information.

[4] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets on the Consolidated Balance Sheets. Reclassifications have been made to previously reported amounts for comparability. See Note 9, "Other Assets," for additional information.

[5] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets on the Consolidated Balance Sheets. Reclassifications have been made to previously reported amounts for comparability. See Note 9, "Other Assets," for additional information.

[6] Amount represents the net of IRLC assets and liabilities and includes the derivative liability associated with the Company's sale of Visa shares. Refer to the "Trading Liabilities and Derivative Instruments" section herein for a discussion of valuation assumptions related to the Visa derivative liability.

[7] Amount represents the net of IRLC assets and liabilities and includes the derivative liability associated with the Company's sale of Visa shares. Refer to the "Trading Liabilities and Derivative Instruments" section herein for a discussion of valuation assumptions related to the Visa derivative liability.