Accumulated Other Comprehensive Income (Loss) Reclassifications in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income, net	$ 7	$ 56	$ 38
Provision for (benefit from) income taxes, investments	258	(138)	(298)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period	(2)	51	1
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of pension and other post-retirement items	(2)	(2)	(3)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period	(2)	(1)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of pension and other post-retirement items	(2)	(2)	(3)
Benefit from income taxes	0	1	1
Total reclassifications for the period	(2)	(1)	(2)
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other income, net	0	54	4
Provision for (benefit from) income taxes, investments	0	(2)	(1)
Income (Loss) from Continuing Operations, including portion attributable to noncontrolling interest	$ 0	$ 52	$ 3