Schedule II - Condensed Financial Information, Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Cash Flows from Operating Activities
Shareholders' net income	$ 547	$ 534	$ 1,668	$ 1,635
Adjustments to reconcile shareholders' net income to net cash provided by (used in) operating activities:
Other liabilities			219	(39)
Other, net			(82)	(75)
Net cash provided by / (used in) operating activities			1,719	1,472
Cash Flows from Investing Activities
Other, net			0	(24)
Net cash provided by/ (used in) investing activities			(297)	(1,405)
Cash Flows from Financing Activities
Net change in short-term debt			(15)	(104)
Net proceeds on issuance of long-term debt			894	0
Repayment of long-term debt			(938)	0
Issuance of common stock			136	93
Repurchase of common stock			(536)	(1,256)
Net cash provided by / (used in) financing activities			(425)	(1,224)
Net increase (decrease) in cash and cash equivalents			961	(1,174)
Cash and cash equivalents, January 1			1,420	2,795
Cash and cash equivalents, September 30	$ 2,381	$ 1,621	$ 2,381	$ 1,621