Fair Value (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 1,839	$ 839
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	18	0
Loans and Leases Receivable, Net Amount	117,585	117,800
Nonmarketable equity securities	1,065	1,046
Deposits	90,116	79,022
Short-term Debt	10,175	12,673
Long-term Debt	45,122	54,128
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,839	839
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	9
Loans and Leases Receivable, Net Amount	117,585	117,800
Nonmarketable equity securities	1,053	1,046
Deposits	90,116	79,022
Short-term Debt	10,175	12,673
Long-term Debt	45,122	54,128
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	1,807	789
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	9
Loans and Leases Receivable, Net Amount	119,498	118,750
Nonmarketable equity securities	1,052	1,067
Deposits	88,151	78,469
Short-term Debt	10,177	12,675
Long-term Debt	47,656	56,120
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 Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Net Amount	0	0
Nonmarketable equity securities	0	0
Deposits	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	1,807	789
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Net Amount	0	0
Nonmarketable equity securities	1,026	1,012
Deposits	0	0
Short-term Debt	0	0
Long-term Debt	29,776	22,036
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 Receivable Held-for-sale, Net, Not Part of Disposal Group	9
Loans and Leases Receivable, Net Amount	119,498	118,750
Nonmarketable equity securities	26	55
Deposits	88,151	78,469
Short-term Debt	10,177	12,675
Long-term Debt	17,880	$ 34,084
Equity Securities [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nonmarketable equity securities	12
Equity Securities [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nonmarketable equity securities	$ 35