Consolidated Statements of Cash Flows - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities
Net Income		$ 2,232	$ 1,843	$ 2,077
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization		566	610	585
Realized investment (gains) losses		(237)	(169)	(57)
Deferred income taxes (benefits)		242	74	21
Net changes in assets and liabilities, net of non-operating effects:
Premiums, accounts and notes receivable		(233)	663	(945)
Reinsurance recoverables		214	142	55
Deferred policy acquisition costs		(282)	(213)	(182)
Other assets		(171)	134	16
Insurance liabilities		506	683	657
Accounts payable, accrued expenses and other liabilities		639	124	423
Current income taxes		92	1	(25)
Debt extinguishment costs		321	0	100
Distributions from partnership investments	[1]	161	144	137
Other, net	[2]	36	(10)	71
Net cash provided by (used in) operating activities	[1],[2]	4,086	4,026	2,933
Proceeds from investments sold:
Fixed maturities and equity securities		2,012	1,544	1,555
Investment maturities and repayments:
Fixed maturities and equity securities		2,051	1,755	1,435
Commercial mortgage loans		335	316	640
Other sales, maturities and repayments (primarily short-term and other long-term investments)	[1]	1,702	1,431	1,160
Investments purchased or originated:
Fixed maturities and equity securities		(5,628)	(5,191)	(4,234)
Commercial mortgage loans		(430)	(165)	(500)
Other (primarily short-term and other long-term investments)		(1,065)	(1,698)	(1,183)
Property and equipment purchases, net		(471)	(461)	(510)
Acquisitions, net of cash acquired		(209)	(4)	(99)
Other, net		0	(101)	0
Net cash provided by (used in) investing activities	[1]	(1,703)	(2,574)	(1,736)
Cash Flows from Financing Activities
Deposits and interest credited to contractholder deposit funds		1,230	1,460	1,429
Withdrawals and benefit payments from contractholder deposit funds		(1,363)	(1,362)	(1,359)
Net change in short-term debt		80	(148)	(21)
Payments for debt extinguishment		(313)	0	(87)
Repayment of long-term debt		(1,250)	0	(851)
Net proceeds on issuance of long-term debt		1,581	0	894
Repurchase of common stock		(2,725)	(139)	(671)
Issuance of common stock		131	36	154
Other, net	[2]	(22)	(72)	(97)
Net cash provided by (used in) financing activities	[2]	(2,651)	(225)	(609)
Effect of foreign currency rate changes on cash and cash equivalents		55	(10)	(40)
Net increase / (decrease) in cash and cash equivalents		(213)	1,217	548
Cash and cash equivalents, January 1,		3,185	1,968	1,420
Cash and cash equivalents, December 31,		2,972	3,185	1,968
Supplemental Disclosure of Cash Information:
Income taxes paid, net of refunds		1,036	1,064	1,194
Interest paid		240	244	245
Accounting Standards Update 2016-09 [Member]
Net changes in assets and liabilities, net of non-operating effects:
Other, net		61	72
Net cash provided by (used in) operating activities		61	72
Cash Flows from Financing Activities
Other, net		(61)	(72)
Net cash provided by (used in) financing activities		(61)	(72)
Accounting Standards Update 2016-09 [Member] | Restatement Adjustment [Member]
Net changes in assets and liabilities, net of non-operating effects:
Other, net				79
Net cash provided by (used in) operating activities				79
Cash Flows from Financing Activities
Other, net				(79)
Net cash provided by (used in) financing activities				(79)
Accounting Standards Update 2016-15 [Member]
Net changes in assets and liabilities, net of non-operating effects:
Distributions from partnership investments		161	144
Net cash provided by (used in) operating activities		161	144
Investment maturities and repayments:
Other sales, maturities and repayments (primarily short-term and other long-term investments)		(161)	(144)
Investments purchased or originated:
Net cash provided by (used in) investing activities		$ (161)	$ (144)
Accounting Standards Update 2016-15 [Member] | Restatement Adjustment [Member]
Net changes in assets and liabilities, net of non-operating effects:
Distributions from partnership investments				137
Net cash provided by (used in) operating activities				137
Investment maturities and repayments:
Other sales, maturities and repayments (primarily short-term and other long-term investments)				(137)
Investments purchased or originated:
Net cash provided by (used in) investing activities				$ (137)

[1] As required in adopting ASU 2016-15 in 2016, the Company retrospectively reclassified $137 million of cash distributions of earnings from partnership investments from investing to operating activities in 2015. The comparable amounts reported in operating activities were $161 million in 2017 and $144 million in 2016.

[2] As required in adopting Accounting Standard Update ("ASU") 2016-09 in 2016, the Company retrospectively reclassified $79 million of cash payments from operating to financing activities in 2015. These payments were related to employee tax obligations associated with stock compensation. The comparable amounts reported in financing activities were $61 million in 2017 and $72 million in 2016.