Securities - Amortized Cost, Fair Value, by Contract Maturity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 11,712
Due after one year through five years, amortized cost	26,152
Due after five years through 10 years, amortized cost	57,737
Due after 10 years, amortized cost	134,917
Amortized cost	230,518	$ 235,391
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	11,758
Due after one year through five years, fair value	26,596
Due after five years through 10 years, fair value	58,322
Due after 10 years, fair value	138,803
Fair value	$ 235,479	239,667
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	2.57%
Due after one year through five years, average yield	1.96%
Due after five years through 10 years, average yield	1.73%
Due after 10 years, average yield	3.63%
Average yield	2.91%
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	1,893
Amortized cost	1,893
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	1,912
Available-for-sale securities, equity maturities, fair value, total	$ 1,912
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	0.35%
Average yield	0.35%
Available-for-sale Securities, Maturities, Single Maturity Date, Amortized Cost Basis:
Due in one year or less, amortized cost	$ 11,712
Due after one year through five years, amortized cost	26,152
Due after five years through 10 years, amortized cost	57,737
Due after 10 years, amortized cost	136,810
Amortized cost	232,411	237,458
Available-for-sale Securities, Maturities, Single Maturity Date, Fair Value:
Due in one year or less, fair value	11,758
Due after one year through five years, fair value	26,596
Due after five years through 10 years, fair value	58,322
Due after 10 years, fair value	140,715
Fair value	$ 237,391	241,754
Available For Sale Securities, Maturities, Single Maturity Date, Average Yield:
Due in one year or less, average yield	2.57%
Due after one year through five years, average yield	1.96%
Due after five years through 10 years, average yield	1.73%
Due after 10 years, average yield	3.58%
Available-for-sale securities, maturities, average yield, total	2.89%
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis:
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	1,039
Due after 10 years, amortized cost	46,893
Amortized cost	47,932	49,073
Held-to-maturity Securities, Debt 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	1,102
Due after 10 years, fair value	49,066
Held-to-maturity Securities, Fair Value	$ 50,168	50,587
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Average Yield [Abstract]
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	5.00%
Due after 10 years, average yield	3.99%
Held-to-maturity securities, maturities, average yield, total	4.01%
Supplemental information
US government agencies and US government sponsored enterprises residential mortgage-backed securities estimated duration	5 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	$ 3,700
Due after one year through five years, amortized cost	7,996
Due after five years through 10 years, amortized cost	7,879
Due after 10 years, amortized cost	82,843
Amortized cost	102,418	103,980
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	3,718
Due after one year through five years, fair value	8,121
Due after five years through 10 years, fair value	8,121
Due after 10 years, fair value	84,516
Fair value	$ 104,476	105,582
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	1.54%
Due after one year through five years, average yield	1.89%
Due after five years through 10 years, average yield	3.02%
Due after 10 years, average yield	3.12%
Average yield	2.96%
U.S. Treasury and government agencies
Available-for-sale debt 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	11,027
Due after 10 years, amortized cost	1,251
Amortized cost	12,278	11,202
Available-for-sale debt securities, 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	10,897
Due after 10 years, fair value	1,192
Fair value	$ 12,089	11,036
Available-for-sale debt securities, 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	0.57%
Due after 10 years, average yield	0.55%
Average yield	0.57%
Obligations of U.S. states and municipalities
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 174
Due after one year through five years, amortized cost	778
Due after five years through 10 years, amortized cost	1,428
Due after 10 years, amortized cost	28,491
Amortized cost	30,871	31,328
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	174
Due after one year through five years, fair value	800
Due after five years through 10 years, fair value	1,516
Due after 10 years, fair value	30,860
Fair value	$ 33,350	33,550
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	5.26%
Due after one year through five years, average yield	3.98%
Due after five years through 10 years, average yield	5.39%
Due after 10 years, average yield	6.59%
Average yield	6.46%
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis:
Amortized cost	$ 12,800	12,800
Certificates of deposit
Available-for-sale debt securities, Amortized cost:
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	0
Due after 10 years, amortized cost	0
Amortized cost	52	282
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	53
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	0
Fair value	$ 53	283
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	0.00%
Due after five years through 10 years, average yield	0.00%
Due after 10 years, average yield	0.00%
Average yield	3.28%
Non-U.S. government debt securities
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 5,617
Due after one year through five years, amortized cost	12,438
Due after five years through 10 years, amortized cost	15,792
Due after 10 years, amortized cost	3,003
Amortized cost	36,850	35,864
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	5,628
Due after one year through five years, fair value	12,721
Due after five years through 10 years, fair value	16,369
Due after 10 years, fair value	3,073
Fair value	$ 37,791	36,676
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	3.09%
Due after one year through five years, average yield	1.73%
Due after five years through 10 years, average yield	0.97%
Due after 10 years, average yield	0.71%
Average yield	1.53%
Corporate debt securities
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 2,138
Due after one year through five years, amortized cost	4,067
Due after five years through 10 years, amortized cost	1,741
Due after 10 years, amortized cost	145
Amortized cost	8,091	12,464
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	2,154
Due after one year through five years, fair value	4,072
Due after five years through 10 years, fair value	1,686
Due after 10 years, fair value	139
Fair value	$ 8,051	$ 12,436
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	2.77%
Due after one year through five years, average yield	2.44%
Due after five years through 10 years, average yield	3.27%
Due after 10 years, average yield	3.31%
Average yield	2.72%
Asset-backed securities
Available-for-sale debt securities, Amortized cost:
Due in one year or less, amortized cost	$ 31
Due after one year through five years, amortized cost	873
Due after five years through 10 years, amortized cost	19,870
Due after 10 years, amortized cost	19,184
Amortized cost	39,958
Available-for-sale debt securities, Fair Value:
Due in one year or less, fair value	31
Due after one year through five years, fair value	882
Due after five years through 10 years, fair value	19,733
Due after 10 years, fair value	19,023
Fair value	$ 39,669
Available-for-sale debt securities, Average yield:
Due in one year or less, average yield	0.55%
Due after one year through five years, average yield	1.74%
Due after five years through 10 years, average yield	2.06%
Due after 10 years, average yield	2.10%
Average yield	2.07%