Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions											3 Months Ended		9 Months Ended
	Dec. 01, 2019	Nov. 07, 2019	Oct. 30, 2019	Sep. 09, 2019	Sep. 01, 2019	Jul. 31, 2019	Jun. 30, 2019	Mar. 01, 2019	Jan. 24, 2019	Apr. 29, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											2,836,250		2,836,250		2,606,750
Carrying value											$ 28,363		$ 28,363		$ 26,068
Series P
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											90,000		90,000		90,000
Carrying value											$ 900		$ 900		$ 900
Issue date													Feb. 05, 2013
Contractual rate in effect													5.45%
Dividend declared per share (in dollars per share)											$ 136.25	$ 136.25	$ 408.75	$ 408.75
Series P | Subsequent Event | Forecast
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Contractual rate in effect	5.45%
Redemption of outstanding non-cumulative preferred stock	$ 900
Series P | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Mar. 01, 2018
Series T
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											0		0		92,500
Carrying value											$ 0		$ 0		$ 925
Issue date													Jan. 30, 2014
Contractual rate in effect								6.70%					0.00%
Dividend declared per share (in dollars per share)												167.50	$ 167.50	502.50
Redemption of outstanding non-cumulative preferred stock								$ 925
Series T | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Mar. 01, 2019
Series W
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											0		0		88,000
Carrying value											$ 0		$ 0		$ 880
Issue date													Jun. 23, 2014
Contractual rate in effect					6.30%								0.00%
Dividend declared per share (in dollars per share)												157.50	$ 472.50	472.50
Redemption of outstanding non-cumulative preferred stock					$ 880
Series W | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Sep. 01, 2019
Series Y
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											143,000		143,000		143,000
Carrying value											$ 1,430		$ 1,430		$ 1,430
Issue date													Feb. 12, 2015
Contractual rate in effect													6.125%
Dividend declared per share (in dollars per share)											$ 153.13	153.13	$ 459.39	459.39
Series Y | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Mar. 01, 2020
Series AA
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											142,500		142,500		142,500
Carrying value											$ 1,425		$ 1,425		$ 1,425
Issue date													Jun. 04, 2015
Contractual rate in effect													6.10%
Dividend declared per share (in dollars per share)											$ 152.50	152.50	$ 457.50	457.50
Series AA | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Sep. 01, 2020
Series BB
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											115,000		115,000		115,000
Carrying value											$ 1,150		$ 1,150		$ 1,150
Issue date													Jul. 29, 2015
Contractual rate in effect													6.15%
Dividend declared per share (in dollars per share)											$ 153.75	153.75	$ 461.25	461.25
Series BB | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Sep. 01, 2020
Series DD
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											169,625		169,625		169,625
Carrying value											$ 1,696		$ 1,696		$ 1,696
Issue date													Sep. 21, 2018
Contractual rate in effect													5.75%
Dividend declared per share (in dollars per share)											$ 143.75		$ 431.25
Series DD | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Dec. 01, 2023
Series EE
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											185,000		185,000		0
Carrying value											$ 1,850		$ 1,850		$ 0
Issue date													Jan. 24, 2019
Contractual rate in effect									6.00%				6.00%
Dividend declared per share (in dollars per share)											$ 150.00		$ 361.67
Preferred stock, shares issued									$ 1,850
Series EE | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Mar. 01, 2024
Series I
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											430,375		430,375		430,375
Carrying value											$ 4,304		$ 4,304		$ 4,304
Issue date													Apr. 23, 2008
Contractual rate in effect										7.90%
Dividend declared per share (in dollars per share)											$ 146.58	148.45	$ 455.09	493.29
Series I | Subsequent Event
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Redemption of outstanding non-cumulative preferred stock			$ 1,370
Series I | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													three-month LIBOR
Preferred stock dividend rate, variable, basis spread													3.47%
Series I | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Apr. 30, 2018
Series Q
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											150,000		150,000		150,000
Carrying value											$ 1,500		$ 1,500		$ 1,500
Issue date													Apr. 23, 2013
Contractual rate in effect													5.15%
Dividend declared per share (in dollars per share)											$ 128.75	128.75	$ 386.25	386.25
Series Q | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													three-month LIBOR
Preferred stock dividend rate, variable, basis spread													3.25%
Series Q | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													May 01, 2023
Series R
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											150,000		150,000		150,000
Carrying value											$ 1,500		$ 1,500		$ 1,500
Issue date													Jul. 29, 2013
Contractual rate in effect													6.00%
Dividend declared per share (in dollars per share)											$ 150.00	150.00	$ 450.00	450.00
Series R | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													three-month LIBOR
Preferred stock dividend rate, variable, basis spread													3.30%
Series R | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Aug. 01, 2023
Series S
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											200,000		200,000		200,000
Carrying value											$ 2,000		$ 2,000		$ 2,000
Issue date													Jan. 22, 2014
Contractual rate in effect													6.75%
Dividend declared per share (in dollars per share)											$ 168.75	168.75	$ 506.25	506.25
Series S | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													three-month LIBOR
Preferred stock dividend rate, variable, basis spread													3.78%
Series S | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Feb. 01, 2024
Series U
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											100,000		100,000		100,000
Carrying value											$ 1,000		$ 1,000		$ 1,000
Issue date													Mar. 10, 2014
Contractual rate in effect													6.125%
Dividend declared per share (in dollars per share)											$ 153.13	153.13	$ 459.38	459.38
Series U | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													three-month LIBOR
Preferred stock dividend rate, variable, basis spread													3.33%
Series U | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Apr. 30, 2024
Series V
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											250,000		250,000		250,000
Carrying value											$ 2,500		$ 2,500		$ 2,500
Issue date													Jun. 09, 2014
Contractual rate in effect							5.00%
Dividend declared per share (in dollars per share)											$ 144.11	125.00	$ 394.11	375.00
Series V | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													three-month LIBOR
Preferred stock dividend rate, variable, basis spread													3.32%
Series V | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Jul. 01, 2019
Series X
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											160,000		160,000		160,000
Carrying value											$ 1,600		$ 1,600		$ 1,600
Issue date													Sep. 23, 2014
Contractual rate in effect													6.10%
Dividend declared per share (in dollars per share)											$ 152.50	152.50	$ 457.50	457.50
Series X | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													three-month LIBOR
Preferred stock dividend rate, variable, basis spread													3.33%
Series X | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Oct. 01, 2024
Series Z
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											200,000		200,000		200,000
Carrying value											$ 2,000		$ 2,000		$ 2,000
Issue date													Apr. 21, 2015
Contractual rate in effect													5.30%
Dividend declared per share (in dollars per share)											$ 132.50	132.50	$ 397.50	397.50
Series Z | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													three-month LIBOR
Preferred stock dividend rate, variable, basis spread													3.80%
Series Z | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													May 01, 2020
Series CC
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											125,750		125,750		125,750
Carrying value											$ 1,258		$ 1,258		$ 1,258
Issue date													Oct. 20, 2017
Contractual rate in effect													4.625%
Dividend declared per share (in dollars per share)											$ 115.63	$ 115.63	$ 346.88	$ 346.88
Series CC | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													three-month LIBOR
Preferred stock dividend rate, variable, basis spread													2.58%
Series CC | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Nov. 01, 2022
Series FF
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											225,000		225,000		0
Carrying value											$ 2,250		$ 2,250		$ 0
Issue date													Jul. 31, 2019
Contractual rate in effect													5.00%
Dividend declared per share (in dollars per share)				$ 126.39							$ 126.39		$ 126.39
Preferred stock, shares issued						$ 2,250
Series FF | Term SOFR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, description of basis													Term SOFR
Preferred stock dividend rate, variable, basis spread													3.38%
Series FF | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date													Aug. 01, 2024
Series GG | Subsequent Event | Forecast
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Contractual rate in effect		4.75%
Preferred stock, shares issued		$ 900