Investment Securities - Amortized Costs and Estimated Fair Values (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Available-for-sale securities
Amortized cost	$ 233,034	$ 228,769
Gross unrealized gains	4,094	3,168
Gross unrealized losses	612	1,543
Fair value	236,516	230,394
Held-to-maturity securities
Amortized cost	30,849	31,434
Gross unrealized gains	685	239
Gross unrealized losses	78	215
Fair value	31,456	31,458
Total investment securities
Amortized cost	263,883	260,203
Gross unrealized gains	4,779	3,407
Gross unrealized losses	690	1,758
Fair value	267,972	261,852
Total mortgage-backed securities
Available-for-sale securities
Amortized cost	90,756	84,190
Gross unrealized gains	1,401	788
Gross unrealized losses	434	1,158
Fair value	91,723	83,820
Held-to-maturity securities
Amortized cost	26,033	26,610
Gross unrealized gains	496	134
Gross unrealized losses	77	200
Fair value	26,452	26,544
U.S. government agencies
Available-for-sale securities
Amortized cost	74,131	69,026
Gross unrealized gains	1,144	594
Gross unrealized losses	352	974
Fair value	74,923	68,646
Held-to-maturity securities
Amortized cost	26,033	26,610
Gross unrealized gains	496	134
Gross unrealized losses	77	200
Fair value	26,452	26,544
Residential: U.S.
Available-for-sale securities
Amortized cost	7,711	5,877
Gross unrealized gains	123	79
Gross unrealized losses	18	31
Fair value	7,816	5,925
Residential: Non-U.S.
Available-for-sale securities
Amortized cost	2,229	2,529
Gross unrealized gains	71	72
Gross unrealized losses	3	6
Fair value	2,297	2,595
Commercial
Available-for-sale securities
Amortized cost	6,685	6,758
Gross unrealized gains	63	43
Gross unrealized losses	61	147
Fair value	6,687	6,654
U.S. Treasury and government agencies
Available-for-sale securities
Amortized cost	58,491	55,771
Gross unrealized gains	302	366
Gross unrealized losses	29	78
Fair value	58,764	56,059
Obligations of U.S. states and municipalities
Available-for-sale securities
Amortized cost	32,649	36,221
Gross unrealized gains	1,847	1,582
Gross unrealized losses	9	80
Fair value	34,487	37,723
Held-to-maturity securities
Amortized cost	4,816	4,824
Gross unrealized gains	189	105
Gross unrealized losses	1	15
Fair value	5,004	4,914
Certificates of deposit
Available-for-sale securities
Amortized cost	75	75
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	75	75
Non-U.S. government debt securities
Available-for-sale securities
Amortized cost	21,608	23,771
Gross unrealized gains	436	351
Gross unrealized losses	9	20
Fair value	22,035	24,102
Corporate debt securities
Available-for-sale securities
Amortized cost	1,750	1,904
Gross unrealized gains	45	23
Gross unrealized losses	3	9
Fair value	1,792	1,918
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Amortized cost	21,037	19,612
Gross unrealized gains	3	1
Gross unrealized losses	111	176
Fair value	20,929	19,437
Asset-backed securities: Other
Available-for-sale securities
Amortized cost	6,668	7,225
Gross unrealized gains	60	57
Gross unrealized losses	17	22
Fair value	6,711	7,260
U.S. government-sponsored enterprise obligations
Available-for-sale securities
Fair value	55,300	50,700
Held-to-maturity securities
Amortized cost	$ 20,400	$ 20,900

Available-for-sale Securities and Held-to-maturity Securities, Accumulated Gross Unrealized Gain, before Tax

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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