Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions											1 Months Ended	2 Months Ended	3 Months Ended		6 Months Ended
	Jul. 29, 2021	Jun. 01, 2021	Apr. 09, 2021	Jun. 09, 2020	May 15, 2020	Apr. 30, 2020	Apr. 13, 2020	Mar. 13, 2020	Mar. 01, 2020	Jan. 08, 2020	Jun. 30, 2021	Jun. 30, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											3,283,750	3,283,750	3,283,750		3,283,750		3,006,250
Carrying value											$ 32,838	$ 32,838	$ 32,838		$ 32,838		$ 30,063
Liquidation value and redemption price per share (in dollars per share)											$ 10,000	$ 10,000	$ 10,000		$ 10,000
Aggregate liquidation value											$ 33,200	$ 33,200	$ 33,200		$ 33,200
Series Y
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											0	0	0		0		0
Carrying value											$ 0	$ 0	$ 0		$ 0		$ 0
Issue date															Feb. 12, 2015
Contractual rate in effect									6.125%						0.00%
Dividend declared per share (in dollars per share)													$ 0	$ 0	$ 0	$ 153.13
Preferred stock redeemed									$ 1,430
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)											0	0	0		0		142,500
Carrying value											$ 0	$ 0	$ 0		$ 0		$ 1,425
Issue date															Jun. 04, 2015
Contractual rate in effect		6.10%													6.10%
Dividend declared per share (in dollars per share)													$ 152.50	152.50	$ 305.00	305.00
Preferred stock redeemed		$ 1,400
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)											0	0	0		0		115,000
Carrying value											$ 0	$ 0	$ 0		$ 0		$ 1,150
Issue date															Jul. 29, 2015
Contractual rate in effect		6.15%													6.15%
Dividend declared per share (in dollars per share)													$ 153.75	153.75	$ 307.50	307.50
Preferred stock redeemed		$ 1,200
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		169,625		169,625
Carrying value											$ 1,696	$ 1,696	$ 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	143.75	$ 287.50	287.50
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	185,000		185,000		185,000
Carrying value											$ 1,850	$ 1,850	$ 1,850		$ 1,850		$ 1,850
Issue date															Jan. 24, 2019
Contractual rate in effect															6.00%
Dividend declared per share (in dollars per share)													$ 150.00	150.00	$ 300.00	300.00
Series EE | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date															Mar. 01, 2024
Series GG
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											90,000	90,000	90,000		90,000		90,000
Carrying value											$ 900	$ 900	$ 900		$ 900		$ 900
Issue date															Nov. 07, 2019
Contractual rate in effect															4.75%
Dividend declared per share (in dollars per share)							$ 118.75			$ 150.42			$ 118.75	118.75	$ 237.50	269.17
Series GG | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date															Dec. 01, 2024
Series JJ
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											150,000	150,000	150,000		150,000		0
Carrying value											$ 1,500	$ 1,500	$ 1,500		$ 1,500		$ 0
Issue date															Mar. 17, 2021
Contractual rate in effect															4.55%
Dividend declared per share (in dollars per share)			$ 93.53										$ 93.53		$ 93.53
Series JJ | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date															Jun. 01, 2026
Series LL
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											185,000	185,000	185,000		185,000		0
Carrying value											$ 1,850	$ 1,850	$ 1,850		$ 1,850		$ 0
Issue date															May 20, 2021
Contractual rate in effect															4.625%
Dividend declared per share (in dollars per share)											$ 0		$ 0		$ 0
Series LL | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date															Jun. 01, 2026
Series I
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											293,375	293,375	293,375		293,375		293,375
Carrying value											$ 2,934	$ 2,934	$ 2,934		$ 2,934		$ 2,934
Issue date															Apr. 23, 2008
Dividend declared per share (in dollars per share)													$ 92.40	106.93	$ 185.46	239.37
Series I | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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		150,000		150,000
Carrying value											$ 1,500	$ 1,500	$ 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	$ 257.50	257.50
Series Q | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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		150,000		150,000
Carrying value											$ 1,500	$ 1,500	$ 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	$ 300.00	300.00
Series R | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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		200,000		200,000
Carrying value											$ 2,000	$ 2,000	$ 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	$ 337.50	337.50
Series S | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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		100,000		100,000
Carrying value											$ 1,000	$ 1,000	$ 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	$ 306.25	306.25
Series U | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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		250,000		250,000
Carrying value											$ 2,500	$ 2,500	$ 2,500		$ 2,500		$ 2,500
Issue date															Jun. 09, 2014
Dividend declared per share (in dollars per share)													$ 89.02	120.16	$ 174.99	250.89
Series V | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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		160,000		160,000
Carrying value											$ 1,600	$ 1,600	$ 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	$ 305.00	305.00
Series X | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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		200,000		200,000
Carrying value											$ 2,000	$ 2,000	$ 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)						$ 265.00							$ 100.50	117.15	$ 201.74	249.65
Series Z | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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		125,750		125,750
Carrying value											$ 1,258	$ 1,258	$ 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	$ 231.25	231.25
Series CC | Three-month LIBOR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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	225,000		225,000		225,000
Carrying value											$ 2,250	$ 2,250	$ 2,250		$ 2,250		$ 2,250
Issue date															Jul. 31, 2019
Contractual rate in effect															5.00%
Dividend declared per share (in dollars per share)													$ 125.00	125.00	$ 250.00	250.00
Series FF | Three-month term SOFR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
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 HH
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											300,000	300,000	300,000		300,000		300,000
Carrying value											$ 3,000	$ 3,000	$ 3,000		$ 3,000		$ 3,000
Issue date															Jan. 23, 2020
Contractual rate in effect															4.60%
Dividend declared per share (in dollars per share)				$ 115.00				$ 125.22					$ 115.00	115.00	$ 230.00	240.22
Series HH | Three-month term SOFR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, basis spread															3.125%
Series HH | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date															Feb. 01, 2025
Series II
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											150,000	150,000	150,000		150,000		150,000
Carrying value											$ 1,500	$ 1,500	$ 1,500		$ 1,500		$ 1,500
Issue date															Feb. 24, 2020
Contractual rate in effect															4.00%
Dividend declared per share (in dollars per share)					$ 141.11								$ 100.00	$ 141.11	$ 200.00	$ 141.11
Series II | Three-month term SOFR
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, basis spread															2.745%
Series II | Five-year CMT
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock dividend rate, variable, basis spread															2.85%
Series II | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date															Apr. 01, 2025
Series KK
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares (in shares)											200,000	200,000	200,000		200,000		0
Carrying value											$ 2,000	$ 2,000	$ 2,000		$ 2,000		$ 0
Issue date															May 12, 2021
Contractual rate in effect															3.65%
Dividend declared per share (in dollars per share)												$ 0	$ 0		$ 0
Series KK | Minimum
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Earliest redemption date															Jun. 01, 2026
Series MM Preferred Stock | Subsequent Event
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Contractual rate in effect	4.20%
Preferred stock issued	$ 2,000