Securities - Amortized Cost, Fair Value, by Contract Maturity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale debt securities, Amortized Cost:
Due in one year or less	$ 11,755
Due after one year through five years	29,328
Due after five years through 10 years	57,612
Due after 10 years	136,696
Amortized cost	235,391	$ 288,466
Available-for-sale debt securities, Fair value
Due in one year or less	12,077
Due after one year through five years	29,769
Due after five years through 10 years	57,803
Due after 10 years	140,018
Fair value	$ 239,667	296,222
Available-for-sale debt securities, Average yield
Due in one year or less	2.85%
Due after one year through five years	2.00%
Due after five years through 10 years	1.63%
Due after 10 years	3.61%
Average yield	2.89%
Available-for-sale equity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	0
Due after five years through 10 years	0
Due after 10 years	2,067
Amortized cost	2,067
Available-for-sale equity securities, Fair value
Due in one year or less	0
Due after one year through five years	0
Due after five years through 10 years	0
Due after 10 years	2,087
Fair value	$ 2,087
Available-for-sale equity securities, Average yield
Due in 1 year or less, average yield	0.00%
Due after 1 year through 5 years, average yield	0.00%
Due after 5 years through 10 years, average yield	0.00%
Due after 10 years, average yield	0.30%
Available-for-sale securities, equity maturities, average yield, total	0.30%
Available-for-sale securities, Amortized cost
Due in 1 year or less, amortized cost	$ 11,755
Due after 1 year through 5 years, amortized cost	29,328
Due after 5 years through 10 years, amortized cost	57,612
Due after 10 years, amortized cost	138,763
Amortized cost	237,458	290,979
Available-for-sale securities, Fair value
Due in 1 year or less, fair value	12,077
Due after 1 year through 5 years, fair value	29,769
Due after 5 years through 10 years, fair value	57,803
Due after 10 years, fair value	142,105
Fair value	$ 241,754	298,752
Available-for-sale securities, Average yield
Due in one year or less	2.85%
Due after one year through five years	2.00%
Due after five years through 10 years	1.63%
Due after 10 years	3.56%
Average yield	2.87%
Held-to-maturity securities, Amortized cost
Due in one year or less	$ 51
Due after one year through five years	0
Due after five years through 10 years	931
Due after 10 years	48,091
Amortized cost	49,073	49,252
Held-to-maturity securities, Fair value
Due in one year or less	50
Due after one year through five years	0
Due after five years through 10 years	976
Due after 10 years	49,561
Fair value	$ 50,587	51,154
Held-to-maturity securities, Average yield
Due in one year or less	4.42%
Due after one year through five years	0.00%
Due after five years through 10 years	5.01%
Due after 10 years	3.98%
Average yield	4.00%
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
Non-agency residential collateralized mortgage obligations estimated duration	4 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	$ 2,415
Due after one year through five years	9,728
Due after five years through 10 years	6,562
Due after 10 years	85,275
Amortized cost	103,980	133,598
Available-for-sale debt securities, Fair value
Due in one year or less	2,421
Due after one year through five years	9,886
Due after five years through 10 years	6,756
Due after 10 years	86,519
Fair value	$ 105,582	137,322
Available-for-sale debt securities, Average yield
Due in one year or less	1.48%
Due after one year through five years	1.86%
Due after five years through 10 years	3.15%
Due after 10 years	3.08%
Average yield	2.93%
U.S. Treasury and government agencies
Available-for-sale debt securities, Amortized Cost:
Due in one year or less	$ 0
Due after one year through five years	0
Due after five years through 10 years	10,069
Due after 10 years	1,133
Amortized cost	11,202	13,603
Available-for-sale debt securities, Fair value
Due in one year or less	0
Due after one year through five years	0
Due after five years through 10 years	9,932
Due after 10 years	1,104
Fair value	$ 11,036	13,645
Available-for-sale debt securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	0.00%
Due after five years through 10 years	0.31%
Due after 10 years	0.48%
Average yield	0.33%
Obligations of U.S. states and municipalities
Available-for-sale debt securities, Amortized Cost:
Due in one year or less	$ 184
Due after one year through five years	754
Due after five years through 10 years	1,520
Due after 10 years	28,870
Amortized cost	31,328	27,841
Available-for-sale debt securities, Fair value
Due in one year or less	187
Due after one year through five years	774
Due after five years through 10 years	1,600
Due after 10 years	30,989
Fair value	$ 33,550	30,068
Available-for-sale debt securities, Average yield
Due in one year or less	5.21%
Due after one year through five years	3.50%
Due after five years through 10 years	5.57%
Due after 10 years	6.68%
Average yield	6.54%
Held-to-maturity securities, Amortized cost
Amortized cost	$ 12,800	10,200
Certificates of deposit
Available-for-sale debt securities, Amortized Cost:
Due in one year or less	230
Due after one year through five years	52
Due after five years through 10 years	0
Due after 10 years	0
Amortized cost	282	1,103
Available-for-sale debt securities, Fair value
Due in one year or less	231
Due after one year through five years	52
Due after five years through 10 years	0
Due after 10 years	0
Fair value	$ 283	1,103
Available-for-sale debt securities, Average yield
Due in one year or less	8.66%
Due after one year through five years	3.28%
Due after five years through 10 years	0.00%
Due after 10 years	0.00%
Average yield	7.68%
Non-U.S. government debt securities
Available-for-sale debt securities, Amortized Cost:
Due in one year or less	$ 6,126
Due after one year through five years	11,177
Due after five years through 10 years	16,575
Due after 10 years	1,986
Amortized cost	35,864	51,492
Available-for-sale debt securities, Fair value
Due in one year or less	6,422
Due after one year through five years	11,429
Due after five years through 10 years	16,747
Due after 10 years	2,078
Fair value	$ 36,676	52,743
Available-for-sale debt securities, Average yield
Due in one year or less	3.11%
Due after one year through five years	1.84%
Due after five years through 10 years	1.06%
Due after 10 years	0.67%
Average yield	1.63%
Corporate debt securities
Available-for-sale debt securities, Amortized Cost:
Due in one year or less	$ 2,761
Due after one year through five years	7,175
Due after five years through 10 years	2,385
Due after 10 years	143
Amortized cost	12,464	18,158
Available-for-sale debt securities, Fair value
Due in one year or less	2,776
Due after one year through five years	7,179
Due after five years through 10 years	2,347
Due after 10 years	134
Fair value	$ 12,436	$ 18,532
Available-for-sale debt securities, Average yield
Due in one year or less	2.87%
Due after one year through five years	2.32%
Due after five years through 10 years	3.09%
Due after 10 years	4.46%
Average yield	2.61%
Asset-backed securities
Available-for-sale debt securities, Amortized Cost:
Due in one year or less	$ 39
Due after one year through five years	442
Due after five years through 10 years	20,501
Due after 10 years	19,289
Amortized cost	40,271
Available-for-sale debt securities, Fair value
Due in one year or less	40
Due after one year through five years	449
Due after five years through 10 years	20,421
Due after 10 years	19,194
Fair value	$ 40,104
Available-for-sale debt securities, Average yield
Due in one year or less	0.71%
Due after one year through five years	1.72%
Due after five years through 10 years	1.79%
Due after 10 years	1.84%
Average yield	1.81%