Shareholders' Equity, Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	$ 19,398	$ 18,413	$ 19,181	$ 21,930
Other comprehensive income (loss)	(153)	259	(438)	343
Balance	19,130	18,620	19,130	18,620
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	327	5	581	(68)
Other comprehensive income (loss) before reclassifications, after tax	(150)	267	(399)	284
Reclassification of (income) losses from accumulated other comprehensive income, after tax	(3)	(8)	(39)	59
Other comprehensive income (loss)	(153)	259	(438)	343
Amounts attributable to noncontrolling interests	17	(26)	48	(37)
Balance	191	238	191	238
Net Unrealized Gains (Losses) on Investments with an Allowance for Credit Losses [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	0	(8)	0	0
Other comprehensive income (loss) before reclassifications, after tax		2	(2)	(48)
Reclassification of (income) losses from accumulated other comprehensive income, after tax		4	2	45
Other comprehensive income (loss)		6	0	(3)
Amounts attributable to noncontrolling interests		(1)
Balance	0	(3)	0	(3)
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	0	0	1	13
Reclassification of (income) losses from accumulated other comprehensive income, tax	0	(1)	(1)	(12)
Net Unrealized Gains (Losses) on Other Investments [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	1,271	1,050	1,563	918
Other comprehensive income (loss) before reclassifications, after tax	(121)	231	(391)	374
Reclassification of (income) losses from accumulated other comprehensive income, after tax	(17)	(24)	(74)	(20)
Other comprehensive income (loss)	(138)	207	(465)	354
Amounts attributable to noncontrolling interests	14	(22)	49	(37)
Balance	1,147	1,235	1,147	1,235
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	32	(63)	104	(97)
Reclassification of (income) losses from accumulated other comprehensive income, tax	5	7	20	5
Unrealized Gains (Losses) on Cash Flow Hedges [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(11)	(25)	(23)	(6)
Other comprehensive income (loss) before reclassifications, after tax	1	(2)	12	(22)
Reclassification of (income) losses from accumulated other comprehensive income, after tax	1	3	2	4
Other comprehensive income (loss)	2	1	14	(18)
Balance	(9)	(24)	(9)	(24)
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	0	0	(3)	8
Reclassification of (income) losses from accumulated other comprehensive income, tax	0	0	(2)	(1)
Pension and Postretirement Benefits [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(863)	(837)	(877)	(855)
Other comprehensive income (loss) before reclassifications, after tax	3	(2)	1	(3)
Reclassification of (income) losses from accumulated other comprehensive income, after tax	13	9	31	30
Other comprehensive income (loss)	16	7	32	27
Amounts attributable to noncontrolling interests	(1)		(3)	(2)
Balance	(848)	(830)	(848)	(830)
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	0	0	0	0
Reclassification of (income) losses from accumulated other comprehensive income, tax	(2)	(3)	(7)	(8)
Foreign Currency Translation [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance	(70)	(175)	(82)	(125)
Other comprehensive income (loss) before reclassifications, after tax	(33)	38	(19)	(17)
Other comprehensive income (loss)	(33)	38	(19)	(17)
Amounts attributable to noncontrolling interests	4	(3)	2	2
Balance	(99)	(140)	(99)	(140)
Other Comprehensive Income (Loss), Tax [Abstract]
Other comprehensive income (loss) before reclassifications, tax	0	0	0	0
Reclassification of (income) losses from accumulated other comprehensive income, tax	$ 0	$ 0	$ 0	$ 0