Investment Securities - Amortized Costs and Estimated Fair Values (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale securities
Amortized cost	$ 271,426	$ 228,769
Gross unrealized gains	5,287	3,168
Gross unrealized losses	356	1,543
Fair value	276,357	230,394
Held-to-maturity securities
Amortized cost	30,907	31,434
Gross unrealized gains	1,177	239
Gross unrealized losses	12	215
Fair value	32,072	31,458
Total investment securities
Amortized cost	302,333	260,203
Gross unrealized gains	6,464	3,407
Gross unrealized losses	368	1,758
Fair value	308,429	261,852
Total mortgage-backed securities
Available-for-sale securities
Amortized cost	113,039	84,190
Gross unrealized gains	2,410	788
Gross unrealized losses	104	1,158
Fair value	115,345	83,820
Held-to-maturity securities
Amortized cost	26,097	26,610
Gross unrealized gains	915	134
Gross unrealized losses	12	200
Fair value	27,000	26,544
Total mortgage-backed securities \| Fannie Mae
Total investment securities
Securities exceeding 10% of total stockholders' equity, Amortized cost	59,700
Securities exceeding 10% of total stockholders' equity, Fair value	61,400
Total mortgage-backed securities \| Freddie Mac
Total investment securities
Securities exceeding 10% of total stockholders' equity, Amortized cost	29,200
Securities exceeding 10% of total stockholders' equity, Fair value	30,000
U.S. government agencies
Available-for-sale securities
Amortized cost	94,723	69,026
Gross unrealized gains	1,979	594
Gross unrealized losses	86	974
Fair value	96,616	68,646
Held-to-maturity securities
Amortized cost	26,097	26,610
Gross unrealized gains	915	134
Gross unrealized losses	12	200
Fair value	27,000	26,544
Residential: U.S.
Available-for-sale securities
Amortized cost	9,872	5,877
Gross unrealized gains	272	79
Gross unrealized losses	5	31
Fair value	10,139	5,925
Residential: Non-U.S.
Available-for-sale securities
Amortized cost	2,534	2,529
Gross unrealized gains	69	72
Gross unrealized losses	2	6
Fair value	2,601	2,595
Commercial
Available-for-sale securities
Amortized cost	5,910	6,758
Gross unrealized gains	90	43
Gross unrealized losses	11	147
Fair value	5,989	6,654
U.S. Treasury and government agencies
Available-for-sale securities
Amortized cost	73,919	55,771
Gross unrealized gains	240	366
Gross unrealized losses	169	78
Fair value	73,990	56,059
Obligations of U.S. states and municipalities
Available-for-sale securities
Amortized cost	29,869	36,221
Gross unrealized gains	2,033	1,582
Gross unrealized losses	1	80
Fair value	31,901	37,723
Held-to-maturity securities
Amortized cost	4,810	4,824
Gross unrealized gains	262	105
Gross unrealized losses	0	15
Fair value	5,072	4,914
Certificates of deposit
Available-for-sale securities
Amortized cost	74	75
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	74	75
Non-U.S. government debt securities
Available-for-sale securities
Amortized cost	22,017	23,771
Gross unrealized gains	483	351
Gross unrealized losses	8	20
Fair value	22,492	24,102
Corporate debt securities
Available-for-sale securities
Amortized cost	1,736	1,904
Gross unrealized gains	44	23
Gross unrealized losses	2	9
Fair value	1,778	1,918
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Amortized cost	24,827	19,612
Gross unrealized gains	16	1
Gross unrealized losses	62	176
Fair value	24,781	19,437
Asset-backed securities: Other
Available-for-sale securities
Amortized cost	5,945	7,225
Gross unrealized gains	61	57
Gross unrealized losses	10	22
Fair value	5,996	7,260
U.S. government-sponsored enterprise obligations
Available-for-sale securities
Fair value	69,800	50,700
Held-to-maturity securities
Amortized cost	$ 20,700	$ 20,900

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