Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions											12 Months Ended
	Mar. 01, 2019	Jan. 24, 2019	Dec. 14, 2018	Oct. 30, 2018	Sep. 21, 2018	Sep. 14, 2018	Jun. 15, 2018	Apr. 29, 2018	Dec. 01, 2017	Oct. 20, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares of preferred stock authorized to issue, in one or more series (in shares)											200,000,000	200,000,000
Preferred stock, par value (in dollars per share)											$ 1.00	$ 1.00
Shares (in shares)											2,606,750	2,606,750
Carrying value											$ 26,068	$ 26,068
Liquidation value and redemption price per share (in dollars per share)											$ 10,000
Series P
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											90,000	90,000
Carrying value											$ 900	$ 900
Issue date											Feb. 05, 2013
Contractual rate in effect											5.45%
Dividend declared per share (in dollars per share)											$ 136.25
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)											92,500	92,500
Carrying value											$ 925	$ 925
Issue date											Jan. 30, 2014
Contractual rate in effect											6.70%
Dividend declared per share (in dollars per share)											$ 167.50
Series T | Scenario, Forecast
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Contractual rate in effect	6.70%
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)											88,000	88,000
Carrying value											$ 880	$ 880
Issue date											Jun. 23, 2014
Contractual rate in effect											6.30%
Dividend declared per share (in dollars per share)											$ 157.50
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
Carrying value											$ 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
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
Carrying value											$ 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
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
Carrying value											$ 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
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	0
Carrying value											$ 1,696	$ 0
Issue date											Sep. 21, 2018
Contractual rate in effect					5.75%						5.75%
Dividend declared per share (in dollars per share)											$ 111.81
Preferred stock, shares issued (in shares)					1,700,000,000
Series DD | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date											Dec. 01, 2023
Series I
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											430,375	600,000
Carrying value											$ 4,304	$ 6,000
Issue date											Apr. 23, 2008
Contractual rate in effect								7.90%
Date at which dividend rate becomes floating											Apr. 30, 2018
Preferred stock dividend rate, variable, description of basis											three-month LIBOR
Preferred stock dividend rate, variable, basis spread											3.47%
Dividend declared per share (in dollars per share)			$ 153.09			$ 148.45	$ 147.34	$ 395.00
Redemption of outstanding non-cumulative preferred stock				$ 1,700
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
Carrying value											$ 1,500	$ 1,500
Issue date											Apr. 23, 2013
Contractual rate in effect											5.15%
Date at which dividend rate becomes floating											May 01, 2023
Preferred stock dividend rate, variable, description of basis											three-month LIBOR
Preferred stock dividend rate, variable, basis spread											3.25%
Dividend declared per share (in dollars per share)											$ 257.50
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
Carrying value											$ 1,500	$ 1,500
Issue date											Jul. 29, 2013
Contractual rate in effect											6.00%
Date at which dividend rate becomes floating											Aug. 01, 2023
Preferred stock dividend rate, variable, description of basis											three-month LIBOR
Preferred stock dividend rate, variable, basis spread											3.30%
Dividend declared per share (in dollars per share)											$ 300.00
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
Carrying value											$ 2,000	$ 2,000
Issue date											Jan. 22, 2014
Contractual rate in effect											6.75%
Date at which dividend rate becomes floating											Feb. 01, 2024
Preferred stock dividend rate, variable, description of basis											three-month LIBOR
Preferred stock dividend rate, variable, basis spread											3.78%
Dividend declared per share (in dollars per share)											$ 337.50
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
Carrying value											$ 1,000	$ 1,000
Issue date											Mar. 10, 2014
Contractual rate in effect											6.125%
Date at which dividend rate becomes floating											Apr. 30, 2024
Preferred stock dividend rate, variable, description of basis											three-month LIBOR
Preferred stock dividend rate, variable, basis spread											3.33%
Dividend declared per share (in dollars per share)											$ 306.25
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
Carrying value											$ 2,500	$ 2,500
Issue date											Jun. 09, 2014
Contractual rate in effect											5.00%
Date at which dividend rate becomes floating											Jul. 01, 2019
Preferred stock dividend rate, variable, description of basis											three-month LIBOR
Preferred stock dividend rate, variable, basis spread											3.32%
Dividend declared per share (in dollars per share)											$ 250.00
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
Carrying value											$ 1,600	$ 1,600
Issue date											Sep. 23, 2014
Contractual rate in effect											6.10%
Date at which dividend rate becomes floating											Oct. 01, 2024
Preferred stock dividend rate, variable, description of basis											three-month LIBOR
Preferred stock dividend rate, variable, basis spread											3.33%
Dividend declared per share (in dollars per share)											$ 305.00
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
Carrying value											$ 2,000	$ 2,000
Issue date											Apr. 21, 2015
Contractual rate in effect											5.30%
Date at which dividend rate becomes floating											May 01, 2020
Preferred stock dividend rate, variable, description of basis											three-month LIBOR
Preferred stock dividend rate, variable, basis spread											3.80%
Dividend declared per share (in dollars per share)											$ 265.00
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
Carrying value											$ 1,258	$ 1,258
Issue date											Oct. 20, 2017
Contractual rate in effect										4.625%	4.625%
Date at which dividend rate becomes floating											Nov. 01, 2022
Preferred stock dividend rate, variable, description of basis											three-month LIBOR
Preferred stock dividend rate, variable, basis spread											2.58%
Dividend declared per share (in dollars per share)											$ 231.25
Preferred stock, shares issued (in shares)										1,300,000,000
Series CC | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date											Nov. 01, 2022
Series EE | Subsequent Event
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Contractual rate in effect		6.00%
Preferred stock, shares issued (in shares)		1,850,000,000
Series O
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Contractual rate in effect									5.50%
Dividend declared per share (in dollars per share)												$ 137.50	$ 137.50
Redemption of outstanding non-cumulative preferred stock									$ 1,300