Securities - Amortized Cost, Fair Value, by Contract Maturity (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 14,178
Due after one year through five years, amortized cost	32,008
Due after five years through 10 years, amortized cost	58,058
Due after 10 years, amortized cost	144,531
Amortized cost	248,775	$ 288,466
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	14,454
Due after one year through five years, fair value	32,538
Due after five years through 10 years, fair value	58,489
Due after 10 years, fair value	148,405
Fair value	$ 253,886	296,222
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	2.69%
Due after one year through five years, average yield	1.93%
Due after five years through 10 years, average yield	1.57%
Due after 10 years, average yield	3.47%
Average yield	2.78%
Available-for-sale equity securities, Amortized cost:
Due in one year or less, amortized cost	$ 0
Due after one year through five years, amortized cost	0
Due after five years through 10 years, amortized cost	0
Due after 10 years, amortized cost	2,587
Amortized cost	2,587
Available-for-sale Securities, Equity Maturities, Single Maturity Date, Fair Value:
Due in one year or less, fair value	0
Due after one year through five years, fair value	0
Due after five years through 10 years, fair value	0
Due after 10 years, fair value	2,605
Available-for-sale securities, equity maturities, fair value, total	$ 2,605
Available For Sale Securities, Equity Maturities, Single Maturity Date, Average Yield:
Due in one year or less, average yield	0.00%
Due after one year through five years, average yield	0.00%
Due after five years through 10 years, average yield	0.00%
Due after 10 years, average yield	0.02%
Average yield	0.02%
Available-for-sale Securities, Maturities, Single Maturity Date, Amortized Cost Basis:
Due in one year or less, amortized cost	$ 14,178
Due after one year through five years, amortized cost	32,008
Due after five years through 10 years, amortized cost	58,058
Due after 10 years, amortized cost	147,118
Amortized cost	251,362	290,979
Available-for-sale Securities, Maturities, Single Maturity Date, Fair Value:
Due in one year or less, fair value	14,454
Due after one year through five years, fair value	32,538
Due after five years through 10 years, fair value	58,489
Due after 10 years, fair value	151,010
Fair value	$ 256,491	298,752
Available For Sale Securities, Maturities, Single Maturity Date, Average Yield:
Due in one year or less, average yield	2.69%
Due after one year through five years, average yield	1.93%
Due after five years through 10 years, average yield	1.57%
Due after 10 years, average yield	3.41%
Available-for-sale securities, maturities, average yield, total	2.75%
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis:
Due in one year or less, amortized cost	$ 52
Due after one year through five years, amortized cost	0
Due after five years through 10 years, amortized cost	901
Due after 10 years, amortized cost	49,216
Amortized cost	50,169	49,252
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value:
Due in one year or less, fair value	52
Due after one year through five years, fair value	0
Due after five years through 10 years, fair value	942
Due after 10 years, fair value	50,851
Held-to-maturity Securities, Fair Value	$ 51,845	51,154
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Average Yield [Abstract]
Due in one year or less, average yield	4.41%
Due after one year through five years, average yield	0.00%
Due after five years through 10 years, average yield	4.98%
Due after 10 years, average yield	3.97%
Held-to-maturity securities, maturities, average yield, total	3.99%
Supplemental information
US government agencies and US government sponsored enterprises residential mortgage-backed securities estimated duration	6 years
US government agencies and US government sponsored enterprises residential collateralized mortgage obligations estimated duration	2 years
U.S. nonagency residential collateralized mortgage obligations estimated duration	3 years
Minimum
Supplemental information
Due period of mortgage-backed securities and collateralized mortgage obligations	10 years
Mortgage-backed securities
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 2,333
Due after one year through five years, amortized cost	10,991
Due after five years through 10 years, amortized cost	6,054
Due after 10 years, amortized cost	92,138
Amortized cost	111,516	133,598
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	2,344
Due after one year through five years, fair value	11,184
Due after five years through 10 years, fair value	6,263
Due after 10 years, fair value	94,285
Fair value	$ 114,076	137,322
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	1.40%
Due after one year through five years, average yield	1.76%
Due after five years through 10 years, average yield	3.23%
Due after 10 years, average yield	2.95%
Average yield	2.81%
U.S. Treasury and government agencies
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 100
Due after one year through five years, amortized cost	0
Due after five years through 10 years, amortized cost	10,228
Due after 10 years, amortized cost	1,154
Amortized cost	11,482	13,603
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	100
Due after one year through five years, fair value	0
Due after five years through 10 years, fair value	10,121
Due after 10 years, fair value	1,126
Fair value	$ 11,347	13,645
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	0.13%
Due after one year through five years, average yield	0.00%
Due after five years through 10 years, average yield	0.22%
Due after 10 years, average yield	0.43%
Average yield	0.24%
Obligations of U.S. states and municipalities
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 139
Due after one year through five years, amortized cost	765
Due after five years through 10 years, amortized cost	1,440
Due after 10 years, amortized cost	28,579
Amortized cost	30,923	27,841
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	142
Due after one year through five years, fair value	788
Due after five years through 10 years, fair value	1,513
Due after 10 years, fair value	30,266
Fair value	$ 32,709	30,068
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	6.55%
Due after one year through five years, average yield	3.39%
Due after five years through 10 years, average yield	5.43%
Due after 10 years, average yield	6.68%
Average yield	6.54%
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis:
Amortized cost	$ 12,700	10,200
Certificates of deposit
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	364
Due after one year through five years, amortized cost	51
Due after five years through 10 years, amortized cost	0
Due after 10 years, amortized cost	0
Amortized cost	415	1,103
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	365
Due after one year through five years, fair value	53
Due after five years through 10 years, fair value	0
Due after 10 years, fair value	0
Fair value	$ 418	1,103
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	5.69%
Due after one year through five years, average yield	3.28%
Due after five years through 10 years, average yield	0.00%
Due after 10 years, average yield	0.00%
Average yield	5.39%
Non-U.S. government debt securities
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 7,243
Due after one year through five years, amortized cost	11,485
Due after five years through 10 years, amortized cost	17,299
Due after 10 years, amortized cost	2,170
Amortized cost	38,197	51,492
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	7,479
Due after one year through five years, fair value	11,750
Due after five years through 10 years, fair value	17,607
Due after 10 years, fair value	2,284
Fair value	$ 39,120	52,743
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	3.28%
Due after one year through five years, average yield	1.75%
Due after five years through 10 years, average yield	1.05%
Due after 10 years, average yield	0.72%
Average yield	1.64%
Corporate debt securities
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 3,486
Due after one year through five years, amortized cost	8,243
Due after five years through 10 years, amortized cost	2,875
Due after 10 years, amortized cost	143
Amortized cost	14,747	18,158
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	3,510
Due after one year through five years, fair value	8,287
Due after five years through 10 years, fair value	2,846
Due after 10 years, fair value	138
Fair value	$ 14,781	$ 18,532
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	2.18%
Due after one year through five years, average yield	2.29%
Due after five years through 10 years, average yield	2.77%
Due after 10 years, average yield	4.46%
Average yield	2.38%
Asset-backed securities
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 513
Due after one year through five years, amortized cost	473
Due after five years through 10 years, amortized cost	20,162
Due after 10 years, amortized cost	20,347
Amortized cost	41,495
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	514
Due after one year through five years, fair value	476
Due after five years through 10 years, fair value	20,139
Due after 10 years, fair value	20,306
Fair value	$ 41,435
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	0.95%
Due after one year through five years, average yield	1.19%
Due after five years through 10 years, average yield	1.76%
Due after 10 years, average yield	1.79%
Average yield	1.76%