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, 2018	Dec. 31, 2017	Dec. 31, 2016
Federal corporate income tax rate	21.00%			35.00%
Transition tax rate	6.20%
Income Tax Expense (Benefit)			$ 1,179	$ (1,470)	$ 693
Deferred Federal Income Tax Expense (Benefit)			342	(2,373)	(827)
Deferred Tax Liabilities, Investments			2,494	2,772
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	8
Impact of U.S. Tax Reform
Other Adjustments, Amount			78	(1,519)	0
Income Tax Expense (Benefit)			66	(1,620)
Deferred Federal Income Tax Expense (Benefit)			(402)	(1,790)
Alternative Minimum Tax Credits
Deferred Federal Income Tax Expense (Benefit)			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			468	350
Deferred Tax Liabilities, Investments			181
GILTI [Member] | Impact of U.S. Tax Reform
Income Tax Expense (Benefit)			45
Other limited partnership interests
Gross Investment Income, Operating			731	$ 798	$ 478
Other limited partnership interests | Impact of U.S. Tax Reform
Income Tax Expense (Benefit)			(125)
Gross Investment Income, Operating			$ 46