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		77.0
Compensation amortization under share-based plans and other changes		77.0
Reclassification of certain tax effects from adoption of updated accounting guidance			24.0	(24.0)
Net income	$ 1,193.0		1,193.0
Dividends			(406.0)
Other			1.0
Other comprehensive income (loss)	(1,299.0)			(1,299.0)
Treasury stock acquired — share repurchase authorization					(700.0)
Net shares acquired related to employee share-based compensation plans					(51.0)
Balance, end of period at Jun. 30, 2018	22,623.0	23,040.0	34,296.0	(1,688.0)	(33,025.0)
Balance, beginning of year (in shares) at Dec. 31, 2017						271.4
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)						(5.2)
Net shares issued under employee share-based compensation plans (in shares)						1.5
Balance, end of period (in shares) at Jun. 30, 2018						267.7
Balance, beginning of year at Mar. 31, 2018		22,995.0	33,981.0	(1,322.0)	(32,675.0)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		12.0
Compensation amortization under share-based plans and other changes		33.0
Net income	524.0		524.0
Dividends			(209.0)
Other			0.0
Other comprehensive income (loss)	(366.0)			(366.0)
Treasury stock acquired — share repurchase authorization					(350.0)
Net shares acquired related to employee share-based compensation plans					0.0
Balance, end of period at Jun. 30, 2018	22,623.0	23,040.0	34,296.0	(1,688.0)	(33,025.0)
Balance, beginning of year (in shares) at Mar. 31, 2018						270.2
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)						(2.7)
Net shares issued under employee share-based compensation plans (in shares)						0.2
Balance, end of period (in shares) at Jun. 30, 2018						267.7
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		145.0
Compensation amortization under share-based plans and other changes		83.0
Net income	1,353.0		1,353.0
Dividends			(421.0)
Other			(1.0)
Other comprehensive income (loss)	2,065.0			2,065.0
Treasury stock acquired — share repurchase authorization	(750.0)				(750.0)
Net shares acquired related to employee share-based compensation plans	(47.0)				(47.0)
Balance, end of period at Jun. 30, 2019	$ 25,321.0	23,372.0	36,135.0	206.0	(34,392.0)
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)	(5.5)					(5.5)
Net shares issued under employee share-based compensation plans (in shares)						2.2
Balance, end of period (in shares) at Jun. 30, 2019	260.3					260.3
Balance, beginning of year at Mar. 31, 2019		23,243.0	35,795.0	(682.0)	(34,016.0)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		91.0
Compensation amortization under share-based plans and other changes		38.0
Net income	$ 557.0		557.0
Dividends			(217.0)
Other			0.0
Other comprehensive income (loss)	888.0			888.0
Treasury stock acquired — share repurchase authorization	(375.0)				(375.0)
Net shares acquired related to employee share-based compensation plans	(0.5)				(1.0)
Balance, end of period at Jun. 30, 2019	$ 25,321.0	$ 23,372.0	$ 36,135.0	$ 206.0	$ (34,392.0)
Balance, beginning of year (in shares) at Mar. 31, 2019						261.9
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)	(2.6)					(2.6)
Net shares issued under employee share-based compensation plans (in shares)						1.0
Balance, end of period (in shares) at Jun. 30, 2019	260.3					260.3