Total Equity and Other Comprehensive Income (Rollforward of Total Equity) (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2020
Common Stock [Abstract]
Equity, Beginning Balance	$ 53,879.0	$ 49,290.0	$ 54,041.0	$ 49,343.0
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201613Member
Net income	1,103.0	3,655.0	2,929.0	4,570.0
Other comprehensive income (loss), net of tax	173.0	551.0	(1,307.0)	2,270.0
Dividends, Cash [Abstract]
Common	(492.0)	(491.0)	(985.0)	(994.0)
Preferred	(48.0)	(55.0)	(105.0)	(118.0)
Preferred stock discount accretion
Common stock activity	12.0	11.0	12.0	11.0
Treasury stock activity	10.0	14.0	138.0	(1,296.0)
Other	48.0	(27.0)	(38.0)	(167.0)
Equity, Ending Balance	54,685.0	52,948.0	54,685.0	52,948.0	$ 49,343.0
Par value less than $.5 million at each date	$ 0.5	$ 0.5	$ 0.5	0.5	0.5	$ 0.5
Cumulative Effect, Period of Adoption, Adjustment
Common Stock [Abstract]
Equity, Beginning Balance				(671.0)
Dividends, Cash [Abstract]
Equity, Ending Balance					(671.0)
Cumulative Effect, Period of Adoption, Adjusted Balance
Common Stock [Abstract]
Equity, Beginning Balance				$ 48,672.0
Dividends, Cash [Abstract]
Equity, Ending Balance					$ 48,672.0
Common Stock
Common Stock [Abstract]
Beginning Balance (in shares)	425	424	424	433
Treasury stock activity, shares		1	1	(8)
Ending Balance, (in shares)	425	425	425	425	433
Equity, Beginning Balance	$ 2,713.0	$ 2,712.0	$ 2,713.0	$ 2,712.0
Dividends, Cash [Abstract]
Equity, Ending Balance	2,713.0	2,712.0	2,713.0	$ 2,712.0	$ 2,712.0
Common Stock | Cumulative Effect, Period of Adoption, Adjusted Balance
Common Stock [Abstract]
Beginning Balance (in shares)				433
Ending Balance, (in shares)					433
Equity, Beginning Balance				$ 2,712.0
Dividends, Cash [Abstract]
Equity, Ending Balance					$ 2,712.0
Capital Surplus - Preferred Stock
Common Stock [Abstract]
Equity, Beginning Balance	3,518.0	3,994.0	3,517.0	3,993.0
Dividends, Cash [Abstract]
Preferred stock discount accretion	1.0	1.0	2.0	2.0
Equity, Ending Balance	3,519.0	3,995.0	3,519.0	3,995.0	3,993.0
Capital Surplus - Preferred Stock | Cumulative Effect, Period of Adoption, Adjusted Balance
Common Stock [Abstract]
Equity, Beginning Balance				3,993.0
Dividends, Cash [Abstract]
Equity, Ending Balance					3,993.0
Capital Surplus - Common Stock and Other
Common Stock [Abstract]
Equity, Beginning Balance	12,361.0	12,294.0	12,367.0	12,376.0
Dividends, Cash [Abstract]
Common stock activity	12.0	11.0	12.0	11.0
Treasury stock activity	4.0	2.0	73.0	51.0
Other	32.0	(18.0)	(43.0)	(149.0)
Equity, Ending Balance	12,409.0	12,289.0	12,409.0	12,289.0	12,376.0
Capital Surplus - Common Stock and Other | Cumulative Effect, Period of Adoption, Adjusted Balance
Common Stock [Abstract]
Equity, Beginning Balance				12,376.0
Dividends, Cash [Abstract]
Equity, Ending Balance					12,376.0
Retained Earnings
Common Stock [Abstract]
Equity, Beginning Balance	48,113.0	41,885.0	46,848.0	42,215.0
Net income	1,091.0	3,648.0	2,907.0	4,556.0
Dividends, Cash [Abstract]
Common	(492.0)	(491.0)	(985.0)	(994.0)
Preferred	(48.0)	(55.0)	(105.0)	(118.0)
Preferred stock discount accretion	(1.0)	(1.0)	(2.0)	(2.0)
Equity, Ending Balance	48,663.0	44,986.0	48,663.0	44,986.0	42,215.0
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
Common Stock [Abstract]
Equity, Beginning Balance				(671.0)
Dividends, Cash [Abstract]
Equity, Ending Balance					(671.0)
Retained Earnings | Cumulative Effect, Period of Adoption, Adjusted Balance
Common Stock [Abstract]
Equity, Beginning Balance				41,544.0
Dividends, Cash [Abstract]
Equity, Ending Balance					41,544.0
Accumulated Other Comprehensive Income (Loss)
Common Stock [Abstract]
Equity, Beginning Balance	1,290.0	2,518.0	2,770.0	799.0
Other comprehensive income (loss), net of tax	173.0	551.0	(1,307.0)	2,270.0
Dividends, Cash [Abstract]
Equity, Ending Balance	1,463.0	3,069.0	1,463.0	3,069.0	799.0
Accumulated Other Comprehensive Income (Loss) | Cumulative Effect, Period of Adoption, Adjusted Balance
Common Stock [Abstract]
Equity, Beginning Balance				799.0
Dividends, Cash [Abstract]
Equity, Ending Balance					799.0
Treasury Stock
Common Stock [Abstract]
Equity, Beginning Balance	(14,146.0)	(14,140.0)	(14,205.0)	(12,781.0)
Dividends, Cash [Abstract]
Treasury stock activity	6.0	12.0	65.0	(1,347.0)
Equity, Ending Balance	(14,140.0)	(14,128.0)	(14,140.0)	(14,128.0)	(12,781.0)
Treasury Stock | Cumulative Effect, Period of Adoption, Adjusted Balance
Common Stock [Abstract]
Equity, Beginning Balance				(12,781.0)
Dividends, Cash [Abstract]
Equity, Ending Balance					(12,781.0)
Non- controlling Interests
Common Stock [Abstract]
Equity, Beginning Balance	30.0	27.0	31.0	29.0
Net income	12.0	7.0	22.0	14.0
Dividends, Cash [Abstract]
Other	16.0	(9.0)	5.0	(18.0)
Equity, Ending Balance	$ 58.0	$ 25.0	$ 58.0	25.0	29.0
Non- controlling Interests | Cumulative Effect, Period of Adoption, Adjusted Balance
Common Stock [Abstract]
Equity, Beginning Balance				$ 29.0
Dividends, Cash [Abstract]
Equity, Ending Balance					$ 29.0