Schedule II - Condensed Financial Information, Statements of Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Cash Flows from Operating Activities
Shareholders' net income		$ 598	$ 519
Adjustments to reconcile shareholders' net income to net cash provided by (used in) operating activities:
Other liabilities		(186)	(263)
Other, net		(31)	5
Net cash provided by (used in) operating activities	[1]	1,579	921
Cash Flows from Investing Activities
Short term investments purchased		(256)	(198)
Net cash provided by (used in) investing activities	[1]	(117)	(360)
Cash Flows from Financing Activities
Net change in short-term debt		(10)	(6)
Repayment of long-term debt		(250)	0
Issuance of common stock		38	10
Repurchase of common stock		(239)	(139)
Net cash provided by (used in) financing activities		(515)	(146)
Net increase (decrease) in cash and cash equivalents		970	433
Cash and cash equivalents, January 1		3,185	1,968
Cash and cash equivalents, March 31		$ 4,155	$ 2,401

[1] As required in adopting Accounting Standard Update ("ASU") 2016-15, the Company retrospectively reclassified $27 million of cash distributions from partnership earnings from investing to operating activities for the first quarter of 2016. The comparable amount reported in operating activities in 2017 was $45 million. See Note 2 for further discussion.