Income Tax (Impact of U.S. Tax Reform) (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Jan. 01, 2018	Sep. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Federal corporate income tax rate	21.00%				35.00%
Transition tax rate	6.20%
Income Tax Expense (Benefit)			$ 886	$ 1,179	$ (1,470)
Deferred Federal Income Tax Expense (Benefit)			(235)	342	(2,373)
Deferred Tax Liabilities, Investments			4,170	3,854
Other Assets
Transition tax rate	8.00%
Cash and Cash Equivalents
Transition tax rate	15.50%
Compensation and fringe benefits
Deferred Federal Income Tax Expense (Benefit)			0	0	8
Impact of U.S. Tax Reform
Other Adjustments, Amount			(326)	78	(1,519)
Income Tax Expense (Benefit)			(326)	66	(1,620)
Deferred Federal Income Tax Expense (Benefit)			(9)	(402)	(1,790)
Alternative Minimum Tax Credits
Deferred Federal Income Tax Expense (Benefit)			9	0	9
Foreign Tax Authority
Repatriation of Foreign Earnings					444
Foreign Tax Authority | Impact of U.S. Tax Reform
Other Adjustments, Amount		$ 180			170
Repatriation of Foreign Earnings			317	468	350
Deferred Tax Liabilities, Investments			193
GILTI [Member] | Impact of U.S. Tax Reform
Effective Income Tax Rate Reconciliation, Tax Contingency, Foreign, Amount			12
Income Tax Expense (Benefit)			35	45
Other limited partnership interests
Gross Investment Income, Operating			$ 825	731	$ 798
Other limited partnership interests | Impact of U.S. Tax Reform
Income Tax Expense (Benefit)				(125)
Gross Investment Income, Operating				$ 46