Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning			$ (1,082)
Shareholders' other comprehensive income (loss), net of tax	$ (14)	$ 22	(536)	$ 258
Accumulated other comprehensive income (loss), ending	(1,857)		(1,857)
Securities [ Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	(31)	436	389	362
Other comprehensive income (loss) before reclassifications, pre-tax	2	(5)	(553)	163
Other comprehensive income (loss) before reclassifications, tax (expense) benefit	(1)	0	112	(62)
Other comprehensive income (loss) before reclassifications, after-tax	1	(5)	(441)	101
Reclassification adjustment, pre-tax	(1)	(26)	27	(76)
Reclassification adjustment, tax (expense) benefit	0	9	(6)	27
Reclassification adjustment, after-tax	(1)	(17)	21	(49)
Shareholders' other comprehensive income (loss), net of tax	0	(22)	(420)	52
Accumulated other comprehensive income (loss), ending	(31)	414	(31)	414
Securities [ Member] | Previously Reported [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	(31)	436	328	362
Securities [ Member] | Restatement Adjustment [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	0	0	65	0
Securities [ Member] | Restatement Adjustment [Member] | Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	0	0	(4)	0
Derivatives [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	(19)	0	(6)	3
Other comprehensive income (loss) before reclassifications, pre-tax	2	(1)	(14)	(1)
Other comprehensive income (loss) before reclassifications, tax (expense) benefit	0	0	3	0
Other comprehensive income (loss) before reclassifications, after-tax	2	(1)	(11)	(1)
Reclassification adjustment, pre-tax	0	1	0	(3)
Reclassification adjustment, tax (expense) benefit	0	0	0	1
Reclassification adjustment, after-tax	0	1	0	(2)
Shareholders' other comprehensive income (loss), net of tax	2	0	(11)	(3)
Accumulated other comprehensive income (loss), ending	(17)	0	(17)	0
Derivatives [Member] | Previously Reported [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	(19)	0	0	3
Derivatives [Member] | Restatement Adjustment [Member] | Accounting Standards Update 2017-12 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	0	0	(6)	0
Translation of foreign currencies [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	(176)	(230)	(69)	(369)
Other comprehensive income (loss) before reclassifications, pre-tax	(31)	38	(136)	179
Other comprehensive income (loss) before reclassifications, tax (expense) benefit	2	(4)	0	(6)
Other comprehensive income (loss) before reclassifications, after-tax	(29)	34	(136)	173
Accumulated other comprehensive income (loss), ending	(205)	(196)	(205)	(196)
Translation of foreign currencies [Member] | Previously Reported [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	(176)	(230)	(65)	(369)
Translation of foreign currencies [Member] | Restatement Adjustment [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	0	0	(4)	0
Postretirement benefits liability [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	(1,617)	(1,352)	(1,635)	(1,378)
Other comprehensive income (loss) before reclassifications, pre-tax	0	0	(12)	2
Other comprehensive income (loss) before reclassifications, tax (expense) benefit	0	0	3	0
Other comprehensive income (loss) before reclassifications, after-tax	0	0	(9)	2
Reclassification adjustment, tax (expense) benefit	(6)	(6)	(13)	(20)
Reclassification adjustment, after-tax	13	10	40	34
Shareholders' other comprehensive income (loss), net of tax	13	10	31	36
Accumulated other comprehensive income (loss), ending	(1,604)	(1,342)	(1,604)	(1,342)
Postretirement benefits liability [Member] | Previously Reported [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	(1,617)	(1,352)	(1,345)	(1,378)
Postretirement benefits liability [Member] | Restatement Adjustment [Member] | Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning	0	0	(290)	0
Reclassification adjustment for amortization of net losses from past experience and prior service costs [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Reclassification adjustment, pre-tax	19	16	53	48
Reclassification adjustment for settlement losses [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Reclassification adjustment, pre-tax	$ 0	$ 0	$ 0	$ 6