Income Tax (Impact of U.S. Tax Reform) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest									$ 3,536	$ 4,281	$ 5,651
Deferred Federal Income Tax Expense (Benefit)									(2,373)	(827)	194
Income Tax Expense (Benefit)									(1,470)	693	1,590
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 2,315	$ 883	$ 856	$ 952	$ (971)	$ 973	$ 1,686	$ 1,900	5,006	3,588	4,061
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	58,870				$ 67,702				58,870	$ 67,702	$ 68,568	$ 72,715
Impact of U.S. Tax Reform
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest									(289)
Deferred Tax Liabilities, Undistributed Foreign Earnings	170								170
Deferred Federal Income Tax Expense (Benefit)									(1,790)
Income Tax Expense (Benefit)									(1,620)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest									1,331
Income tax (expense) benefit related to items of other comprehensive income (loss)									144
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,475								$ 1,475