Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended
	Apr. 12, 2019	Mar. 01, 2019	Jan. 24, 2019	Mar. 31, 2019	Dec. 31, 2018
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	$ 1
Shares (in shares)				2,699,250	2,606,750
Carrying value				$ 26,993	$ 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)				0	92,500
Carrying value				$ 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
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	169,625
Carrying value				$ 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
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	0
Carrying value				$ 1,850	$ 0
Issue date				Jan. 24, 2019
Contractual rate in effect			6.00%	6.00%
Dividend declared per share (in dollars per share)				$ 0
Preferred stock, shares issued (in shares)			1,850,000,000
Series EE | Subsequent Event
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Dividend declared per share (in dollars per share)	$ 211.67
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
Carrying value				$ 4,304	$ 4,304
Issue date				Apr. 23, 2008
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)				$ 155.51
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)				$ 128.75
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)				$ 150.00
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)				$ 168.75
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)				$ 153.13
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)				$ 125.00
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)				$ 152.50
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)				$ 132.50
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%
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)				$ 115.63
Series CC | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date				Nov. 01, 2022