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Accounting Policies (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
Accounting Policies (Details) - USD ($) $ in Millions	Jan. 01, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings		$ (44,986)		$ (44,986)		$ (42,215)
Held-to-maturity securities, amortized cost		1,441		1,441		17,661
Held-to-maturity securities, fair value		1,615		1,615		18,044
Other comprehensive income (loss), before tax and net of reclassifications into Net income		535	$ 869	2,820	$ 1,767
Available for sale debt securities, amortized cost		93,661		93,661		67,790
Investment securities – available for sale		97,052		97,052		$ 69,163
Accounting Standards Update 2016-13 \| Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 671
Accounting Standards Update 2019-04 \| Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Held-to-maturity securities, amortized cost	(16,200)
Held-to-maturity securities, fair value	(16,500)
Other comprehensive income (loss), before tax and net of reclassifications into Net income	306
Available for sale debt securities, amortized cost	16,200
Investment securities – available for sale	$ 16,500
Accounting Standards Update 2020-04 \| Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Held-to-maturity securities, amortized cost		(49)		(49)
Held-to-maturity securities, fair value		(48)		(48)
Available for sale debt securities, amortized cost		49		49
Investment securities – available for sale		$ 48		$ 48