CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Change in unrealized holding gains on investments, tax expense	$ 121	$ 12	$ 64
Reclassification adjustment for gross gains included in net income, tax expense	23	27	13
Postretirement plans, tax expense	17	22	2
Unrealized gains transferred to noncontrolling interest on sale of life affiliate, tax expense	$ 0	$ 4	$ 0