Fair Value (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 1,967	$ 1,899
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	126	108
Loans and Leases Receivable, Net Amount	124,049	121,617
Nonmarketable equity securities	1,250	1,233
Deposits	97,446	93,256
Short-term Debt	9,564	11,413
Long-term Debt	45,076	44,226
Carrying Value of Deposit Liabilities with no Defined Contractual Maturities		47,400
Fair Value of Deposit Liabilities With No Defined Contractual Maturities		45,200
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,967	1,899
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	119	95
Loans and Leases Receivable, Net Amount	124,049	121,617
Nonmarketable equity securities	1,210	1,233
Deposits	49,025	45,869
Short-term Debt	9,564	11,413
Long-term Debt	45,076	44,226
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,895	1,865
Loans and Leases Receivable, Net Amount	125,530	123,302
Nonmarketable equity securities	1,210	1,239
Short-term Debt	9,567	11,417
Long-term Debt	46,973	46,624
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	0	0
Loans and Leases Receivable, Net Amount	0	0
Nonmarketable equity securities	0	0
Short-term Debt	0	0
Long-term Debt	0	0
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,895	1,865
Loans and Leases Receivable, Net Amount	0	0
Nonmarketable equity securities	1,210	1,190
Short-term Debt	0	0
Long-term Debt	28,384	27,807
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	0	0
Loans and Leases Receivable, Net Amount	125,530	123,302
Nonmarketable equity securities	0	49
Short-term Debt	9,567	11,417
Long-term Debt	18,589	18,817
Portion at Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	119	95
Deposits	48,845	45,827
Portion at Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0	0
Deposits	0	0
Portion at Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0	0
Deposits	0	0
Portion at Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	119	95
Deposits	$ 48,845	$ 45,827

Carrying Value of Deposit Liabilities with no Defined Contractual Maturities

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Fair Value of Deposit Liabilities With No Defined Contractual Maturities

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Nonmarketable equity securities

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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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