Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common stock [Member]	Retained earnings [Member]	Accumulated other comprehensive income (loss), net of tax [Member]	Treasury stock, at cost [Member]	Common shares outstanding [Member]
Shareholders' Equity [Roll Forward]
Cumulative effect of adoption of updated accounting guidance for equity financial instruments			$ 22.0	$ (22.0)
Balance, beginning of year at Dec. 31, 2017		$ 22,886.0	33,462.0	(343.0)	$ (32,274.0)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		93.0
Compensation amortization under share-based plans and other changes		110.0
Reclassification of certain tax effects from adoption of updated accounting guidance			24.0	(24.0)
Net income	$ 1,902.0		1,902.0
Dividends			(613.0)
Other			2.0
Other comprehensive income (loss)	(1,614.0)			(1,614.0)
Treasury stock acquired — share repurchase authorization					(1,100.0)
Net shares acquired related to employee share-based compensation plans					(51.0)
Balance, end of period at Sep. 30, 2018	22,460.0	23,089.0	34,799.0	(2,003.0)	(33,425.0)
Balance, beginning of year (in shares) at Dec. 31, 2017						271.4
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)						(8.2)
Net shares issued under employee share-based compensation plans (in shares)						1.6
Balance, end of period (in shares) at Sep. 30, 2018						264.8
Balance, beginning of year at Jun. 30, 2018		23,040.0	34,296.0	(1,688.0)	(33,025.0)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		16.0
Compensation amortization under share-based plans and other changes		33.0
Net income	709.0		709.0
Dividends			(207.0)
Other			1.0
Other comprehensive income (loss)	(315.0)			(315.0)
Treasury stock acquired — share repurchase authorization					(400.0)
Net shares acquired related to employee share-based compensation plans					0.0
Balance, end of period at Sep. 30, 2018	22,460.0	23,089.0	34,799.0	(2,003.0)	(33,425.0)
Balance, beginning of year (in shares) at Jun. 30, 2018						267.7
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)						(3.0)
Net shares issued under employee share-based compensation plans (in shares)						0.1
Balance, end of period (in shares) at Sep. 30, 2018						264.8
Balance, beginning of year at Dec. 31, 2018	22,894.0	23,144.0	35,204.0	(1,859.0)	(33,595.0)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		173.0
Compensation amortization under share-based plans and other changes		115.0
Net income	1,749.0		1,749.0
Dividends			(636.0)
Other			0.0
Other comprehensive income (loss)	2,484.0			2,484.0
Treasury stock acquired — share repurchase authorization	(1,130.0)				(1,125.0)
Net shares acquired related to employee share-based compensation plans	(47.0)				(47.0)
Balance, end of period at Sep. 30, 2019	$ 25,607.0	23,432.0	36,317.0	625.0	(34,767.0)
Balance, beginning of year (in shares) at Dec. 31, 2018	263.6					263.6
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)	(8.0)					(8.0)
Net shares issued under employee share-based compensation plans (in shares)						2.5
Balance, end of period (in shares) at Sep. 30, 2019	258.1					258.1
Balance, beginning of year at Jun. 30, 2019		23,372.0	36,135.0	206.0	(34,392.0)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		28.0
Compensation amortization under share-based plans and other changes		32.0
Net income	$ 396.0		396.0
Dividends			(215.0)
Other			1.0
Other comprehensive income (loss)	419.0			419.0
Treasury stock acquired — share repurchase authorization	(375.0)				(375.0)
Net shares acquired related to employee share-based compensation plans	(0.1)				0.0
Balance, end of period at Sep. 30, 2019	$ 25,607.0	$ 23,432.0	$ 36,317.0	$ 625.0	$ (34,767.0)
Balance, beginning of year (in shares) at Jun. 30, 2019						260.3
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)	(2.5)					(2.5)
Net shares issued under employee share-based compensation plans (in shares)						0.3
Balance, end of period (in shares) at Sep. 30, 2019	258.1					258.1