Total Equity and Other Comprehensive Income (Rollforward of Total Equity) (Details) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 13, 2021 $ / shares shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($) shares	Sep. 01, 2020 shares	Jun. 30, 2020 USD ($)
Common Stock [Abstract]
Equity, Beginning Balance		$ 54,685.0	$ 52,948.0	$ 54,041.0	$ 49,343.0
Accounting Standards Update [Extensible List]						us-gaap:AccountingStandardsUpdate201613Member
Net income		1,490.0	1,532.0	4,419.0	6,102.0
Other comprehensive income (loss), net of tax		(384.0)	(72.0)	(1,691.0)	2,198.0
Dividends, Cash [Abstract]
Common		(538.0)	(494.0)	(1,523.0)	(1,488.0)
Preferred		(57.0)	(63.0)	(162.0)	(181.0)
Preferred stock discount accretion
Preferred stock issuance		1,489.0		1,489.0
Common stock activity				12.0	11.0
Treasury stock activity		(382.0)	(87.0)	(244.0)	(1,383.0)
Preferred stock redemption			(480.0)		(480.0)
Other		(6.0)	26.0	(44.0)	(141.0)
Equity, Ending Balance		56,297.0	53,310.0	56,297.0	53,310.0	$ 49,343.0
Par value less than $.5 million at each date		$ 0.5	$ 0.5	$ 0.5	0.5	0.5	$ 0.5	$ 0.5		$ 0.5
Common stock held in treasury at cost (shares) | shares		120,000,000		120,000,000				119,000,000
Depositary shares conversion ratio	0.01
Series Q Preferred Stock
Dividends, Cash [Abstract]
Treasury stock, preferred (shares) | shares									4,800
Common stock held in treasury at cost (shares) | shares									19,200,000
Depositary Shares
Dividends, Cash [Abstract]
Common stock held in treasury at cost (shares) | shares									19,200,000
Series T Preferred Stock
Dividends, Cash [Abstract]
Common stock activity (shares) | shares	1,500,000
Fixed interest rate	3.40%
Preferred stock, par or stated value per share (in dollars per share) | $ / shares	$ 1
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) | shares		425,000,000	425,000,000	424,000,000	433,000,000
Treasury stock activity, shares | shares		(2,000,000)	(1,000,000)	(1,000,000)	(9,000,000)
Ending Balance, (in shares) | shares		423,000,000	424,000,000	423,000,000	424,000,000	433,000,000
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) | shares					433,000,000
Ending Balance, (in shares) | shares						433,000,000
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		3,519.0	3,995.0	3,517.0	3,993.0
Dividends, Cash [Abstract]
Preferred stock discount accretion		1.0	1.0	3.0	3.0
Preferred stock issuance		1,489.0		1,489.0
Preferred stock redemption			(480.0)		(480.0)
Equity, Ending Balance		5,009.0	3,516.0	5,009.0	3,516.0	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		12,409.0	12,289.0	12,367.0	12,376.0
Dividends, Cash [Abstract]
Common stock activity				12.0	11.0
Treasury stock activity		5.0	1.0	78.0	52.0
Other		30.0	30.0	(13.0)	(119.0)
Equity, Ending Balance		12,444.0	12,320.0	12,444.0	12,320.0	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		48,663.0	44,986.0	46,848.0	42,215.0
Net income		1,474.0	1,519.0	4,381.0	6,075.0
Dividends, Cash [Abstract]
Common		(538.0)	(494.0)	(1,523.0)	(1,488.0)
Preferred		(57.0)	(63.0)	(162.0)	(181.0)
Preferred stock discount accretion		(1.0)	(1.0)	(3.0)	(3.0)
Equity, Ending Balance		49,541.0	45,947.0	49,541.0	45,947.0	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		1,463.0	3,069.0	2,770.0	799.0
Other comprehensive income (loss), net of tax		(384.0)	(72.0)	(1,691.0)	2,198.0
Dividends, Cash [Abstract]
Equity, Ending Balance		1,079.0	2,997.0	1,079.0	2,997.0	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		(14,140.0)	(14,128.0)	(14,205.0)	(12,781.0)
Dividends, Cash [Abstract]
Treasury stock activity		(387.0)	(88.0)	(322.0)	(1,435.0)
Equity, Ending Balance		(14,527.0)	(14,216.0)	(14,527.0)	(14,216.0)	(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		58.0	25.0	31.0	29.0
Net income		16.0	13.0	38.0	27.0
Dividends, Cash [Abstract]
Other		(36.0)	(4.0)	(31.0)	(22.0)
Equity, Ending Balance		$ 38.0	$ 34.0	$ 38.0	34.0	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